Taqwa is one of the most frequent motifs of the Nahj al-Balaghah. In fact it would be hard to find another book which emphasizes this spiritual term to the extent of this book. Even in the Nahj al-Balaghah, no other term or concept receives so much attention and stress as taqwa. What is taqwa?
Often it is thought that taqwa means piety and abstinence and so implies a negative attitude. In other words, it is maintained that the greater the amount of abstinence, withdrawal, and self-denial, the more perfect is one’s taqwa. According to this interpretation, taqwa is a concept divorced from active life; secondly it is a negative attitude; thirdly, it means that the more severely this negative attitude is exercised, the greater one’s taqwa would be. Accordingly, the sanctimonious professors of taqwa, in order to avoid its being tainted and to protect it from any blemish, withdraw from the bustle of life, keeping themselves away from involvement in any matter or affair of the world.
Undeniably, abstinence and caution exercised with discretion is an essential principle of wholesome living. For, in order to lead a healthy life, man is forced to negate and affirm, deny and posit, renounce and accept, avoid and welcome different things. It is through denial and negation that the positive in life can be realized. It is through renunciation and avoidance that concentration is given to action.
The principle of Tawhid contained in the dictum la ilaha illa Allah is at the same time a negation as well as an affirmation. Without negation of everything other than God it is not possible to arrive at Tawhid. That is why rebellion and surrender, kufr (unbelief) and iman (belief), go together; that is, every surrender requires a rebellion and every faith (iman) calls for a denial and rejection (kufr), and every affirmation implies a negation. The Quran says:
So whoever disbelieves in taghut and believes in God, has laid hold of the most firm bond …. (2:256)
However, firstly, every denial, negation, rejection, and rebellion operates between the limits of two opposites; the negation of one thing implies movement towards its opposite; the rejection of the one marks the beginning of the acceptance of the other. Accordingly, every healthy denial and rejection has both a direction and a goal, and is confined within certain definite limits.
Therefore, a blind practice and purposeless attitude, which has neither direction nor a goal, nor is confined within any limits, is neither defensible nor of any spiritual worth.
Secondly, the meaning of taqwa in the Nahj al-Balaghah is not synonymous with that of ‘abstinence’, even in its logically accepted sense discussed above. Taqwa, on the other hand, according to the Nahj al-Balaghah, is a spiritual faculty which appears as a result of continued exercise and practice. The healthy and rational forms of abstinence are, firstly, the preparatory causes
for the emergence of that spiritual faculty; secondly, they are also its effects and outcome.
This faculty strengthens and vitalizes the soul, giving it a kind of immunity. A person who is devoid of this faculty, if he wants to keep himself free from sins, it is unavoidable for him to keep away from the causes of sin. Since society is never without these causes, inevitably he has to go into seclusion and isolate himself. It follows from this argument that one should either remain pious by isolating himself from one’s environment, or he should enter society and bid farewell to taqwa. Moreover, according to this logic, the more isolated and secluded a person’s life is and the more he abstains from mixing with other people, the greater is his piety and taqwa in the eyes of the common people.
However, if the faculty of taqwa is cultivated inside a person’s soul, it is no longer necessary for him to seclude himself from his environment. He can keep himself clean and uncorrupted without severing his relations with society.
The former kind of persons are like those who take refuge in mountains for fear of some plague or epidemic. The second kind resemble those who acquire immunity and resistance through vaccination and so do not deem it necessary to leave the city and avoid contact with their townsfolk. On the other hand, they hasten to the aid of the suffering sick in order to save them. Sa’di is alluding to the first kind of pious in his Gulistan, when he says:
Saw I a sage in the mountains,
Happy in a cave, far from the world’s tide.
Said I, "Why not to the city return,
And lighten your heart of this burden?"
He said, "The city abounds in tempting beauties,
And even elephants slip where mud is thick."
The Nahj al-Balaghah speaks of taqwa as a spiritual faculty acquired through exercise and assiduity, which on its emergence produces certain characteristic effects, one of which is the ability to abstain from sins with ease.
I guarantee the truth of my words and I am responsible for what I say. If similar events and experiences of the past serve as a lesson for a person, then taqwa prevents him from plunging recklessly into doubts … 
Beware that sins are like unruly horses whose reins have been taken way and which plunge with their riders into hell-fire. But taqwa is like a trained steed whose reins are in the hands of its rider and enters with its rider into Paradise. 
In this sermon taqwa is described as a spiritual condition which results in control and command over one’s self. It explains that the result of subjugation to desires and lusts and being devoid of taqwa degrades one’s personality making it vulnerable to the cravings of the carnal self. In such a state, man is like a helpless rider without any power and control, whom his mount takes wherever it desires. The essence of taqwa lies in possessing a spiritual personality endowed with will-power, and possessing mastery over the domain of one’s self. A man with taqwa is like an expert horseman riding a well-trained horse and who with
complete mastery and control drives his tractable steed in the direction of his choice.
Certainly the taqwa of God assists His awliya (friends) in abstaining from unlawful deeds and instils His fear into their hearts. As a result, their nights are passed in wakefulness and their days in thirst [on account of fasting].
Here Ali (a) makes it clear that taqwa is something which automatically leads to abstention from unlawful actions and to the fear of God, which are its necessary effects. Therefore, according to this view, taqwa is neither itself abstinence nor fear of God; rather, it is a sacred spiritual faculty of which these two are only consequences:
For indeed, today taqwa is a shield and a safeguard, and tomorrow (i.e. in the Hereafter) it shall be the path to Paradise. 
In sermon 157, taqwa is compared to an invincible fortress built on heights which the enemy has no power to infiltrate. Throughout, the emphasis of the Imam (a) lies on the spiritual and psychological aspect of taqwa and its effects upon human spirit involving the emergence of a dislike for sin and corruption and an inclination towards piety, purity, and virtue.
Further illustrations of this view can be cited from the Nahj al-Balaghah, but it seems that the above quotations are sufficient.
Taqwa is Immunity not Restraint
We have already mentioned some of the various elements found in the spiritual advices (mawa’iz) of the Nahj al-Balaghah. We began with taqwa and saw that taqwa, from the viewpoint of the Nahj al-Balaghah, is a sublime spiritual faculty which is the cause of certain attractions and repulsions; i.e. attraction towards edifying spiritual values and repulsion towards degrading materialistic vices. The Nahj al-Balaghah considers taqwa as a spiritual state that gives strength to human personality and makes man the master of his own self.
Taqwa as Immunity
The Nahj al-Balaghah stresses that taqwa is for man a shield and a shelter, not a chain or a prison. There are many who do not distinguish between immunity and restraint, between security and confinement, and promptly advocate the destruction of the sanctuary of taqwa in the name of freedom and liberation from bonds and restraint.
That which is common between a sanctuary and a prison is the existence of a barrier. Whereas the walls of a sanctuary avert dangers, the walls of a prison hinder the inmates from realizing their inner capacities and from benefiting from the bounties of life. Ali (a) clarifies the difference between the two, where he says:
Let it be known to you, O servants of God, that taqwa is a formidable fortress, whereas impiety and corruption is a weak and indefensible enclosure that does not safeguard its people, and does not offer any protection to those who take refuge in it. Indeed, it is only with taqwa that the tentacles of sins and misdeeds can be severed. 
Ali (a), in this sublime advice, compares sins and evil deeds which are afflictions of the human soul to poisonous insects and reptiles, and suggests that the faculty of taqwa is an effective defence against them. In some of his discourses, he makes it clear that taqwa not only does not entail restraint and restriction or is an impediment to freedom, but on the other hand it is the source and fountainhead of all true freedoms. In sermon 230, he says:
Taqwa is the key to guidance, the provision for the next world, the freedom from every kind of slavery, and the deliverance from every form of destruction.
The message is clear. Taqwa gives man spiritual freedom and liberates him from the chains of slavery and servitude to lusts and passions. It releases him from the bonds of envy, lust, and anger, and this expurgates society from all kinds of social bondages and servitudes. Men who are not slaves of comfort, money, power, and glory, never surrender to the various forms of bondage which plague the human society.
The Nahj al-Balaghah deals with the theme of taqwa and its various effects in many of its passages; but we don’t consider it necessary to discuss all of them here. Our main objective here is to discover the meaning of taqwa from the point of view of the Nahj al-Balaghah, so as to unearth the reason for so much emphasis that this book places on this concept.
Of the many effects of taqwa that have been pointed out, two are more important than the rest: firstly, the development of insight and clarity of vision; secondly, the capacity to solve problems and to weather difficulties and crises. We have discussed this in detail elsewhere. Moreover, a discussion of these effects of taqwa here will take us beyond our present aim which is to clarify the true meaning of taqwa. It will not be out of place to call attention to certain profound remarks of the Nahj al-Balaghah about the reciprocal relationship between the human being and taqwa.
A Reciprocal Commitment:
In spite of the great emphasis laid by the Nahj al-Balaghah on taqwa as a kind of guarantee and immunity against sin and temptation, it should be noticed that one must never neglect to safeguard and protect taqwa itself. Taqwa guards man, and man must safeguard his taqwa. This, as we shall presently explain, is not a vicious circle.
This reciprocal guarding of the one by the other is comparable to the one between a person and his clothes. A man takes care of his clothes and protects them from being spoiled or stolen, while the clothes in turn guard him against heat or cold. In fact the Holy Quran speaks of taqwa as a garment:
And the garment of taqwa – that is better. (7:26)
Ali (a), speaking about this relationship of mutual protection between a person and his taqwa, says:
Turn your sleep into wakefulness by the means of taqwa and spend your days in its company. Keep its consciousness alive in your hearts. With it wash away your sins and cure your ailments… Beware, guard your taqwa and place your self under its guard. 
At another place in the same sermon, Ali (a) says:
O God’s servants, I advise you to cultivate the taqwa of God. Indeed it is a right that God has over you and it is through it that you can have any right over God. You should beseech God’s help for guarding it and seek its aid for [fulfilling your duty to] God. 
 Nahj al-Balaghah, Sermon 16 Ibid.  Ibid., Sermon 114  Ibid., Sermon 191  Ibid., Sermon 157  See Guftar e mah, vol. I, the second speech  Nahj al-Balaghah., Khutab 191  Ibid.
Source: Selected excerpt from ‘Glimpses of Nahj al-Balagha‘ by Shaheed Murtadha Mutahhari