اَلتَّقْوى حِصْنُ المُؤْمِنِ
Taqwa is the faithful’s fortress.
Taqwa (تقوى) is defined in Islam as the avoidance of sin. It is roughly translated into the English concept of piety and God-fearing. The Holy Quran says in Surat Al-Baqarah
And take provisions, but indeed, the best provision is fear of Allah
Taqwa is the subject of many sermons by Ali bin Abi Talib. In sermon 156 of Nahjul Balaghah he says:
Know O’ creatures of Allah! that piety is a strong house of protection while impiety is a weak house which does not protect its people, and does not give security to him who takes refuge therein.
And in sermon 189
You should therefore exercise fear of Allah because it has a rope whose twist is strong and its pinnacle is lofty and invulnerable. Hasten toward death in its pangs (by doing good acts) and be prepared for it before its approach, because the ultimate end is the Day of Judgement. This is enough preaching for one who understands and enough of a lesson for one who does not know. What idea do you have, before reaching that end, of the narrowness of grave, the hardship of loneliness, fear of the passage towards the next world, the pangs of fear, the shifting of ribs here and there (due to narrowing of the grave), the deafness of ears, the darkness of the grave, fear of the promised punishment, the closing of the receptacle of the grave and the laying of stones?
And in sermon 197:
Now then, I advise you to fear Allah, Who created you for the first time; towards Him is your return, with Him lies the success of your aims, at Him terminate (all) your desires, towards Him runs your path of right and He is the aim of your fears (for seeking protection). Certainly, fear of Allah is the medicine for your hearts, sight for the blindness of your spirits, the cure for the ailments of your bodies, the rectifier of the evils of your breasts, the purifier of the pollution of your minds, the light of the darkness of your eyes, the consolation for the fear of your heart and the brightness for the gloom of your ignorance.