This is the chronic disease. It is man’s consideration of himself with the eye of self-glorification and self-importance and his consideration of others with the eye of contempt. The result as regards the tongue is that he says, ‘I.. I..’; as accursed Iblis said, ‘I am better than he; Thou hast created me of fire, but him Thou hast created of clay’ (38:77). The fruit of it in society is self-exaltation and self-advancement and the endeavour to be foremost in discussions and resentment when what one says is contradicted. The arrogant man is he who, when he gives advice, mortifies, but, when he receives it, is rude. Every one who considers himself better than one of the creatures of God most high is arrogant. Indeed, you ought to realize that the good man is he who is good in God’s sight in the mansion of eternity; and that is something unknown to man, postponed to the End. Your belief that you are better than others is sheer ignorance. Rather you ought not to look at anyone without considering that he is better than you and superior to you. Thus, if you see a child, you say, ‘This person has never sinned against God, but I have sinned, and so he is better than I.’ And if you see an older person, you say, ‘This man was a servant of God before me, and is certainly better than I.’ If he is a scholar, you say, ‘This man has been given what I have not been given and reached what I did not reach, and knows what I am ignorant of; then how shall I be like him?’ And if he is ignorant, you say, ‘This man has sinned against God in ignorance, and I have sinned against Him knowingly, so God’s case against me is stronger, and I do not know what end He will give to me and what end to him.’ If he is an infidel, you say, ‘I do not know; perhaps he will become a Muslim and his life will end in doing good, and because of his acceptance of Islam something of his sins will be taken away, as a hair is taken from dough; but as for me - God is our refuge (God grant it does not happen) - perhaps God will lead me astray so that I become an infidel and my life ends in doing evil, and then tomorrow he will be among those brought near to God and I shall be among the punished.’
Arrogance will not leave your heart except when you know that the great man is he who is great in the sight of God most high. That is something which cannot be known until the end of life, and there is doubt about that (the end and whether it will be good or bad). So let fear of the end occupy you and keep you from making yourself out, despite the doubt about your end, to be aboved the servants of God most high. Your certitude and faith at present do not exclude the possibility of your changing in the future; for God is the disposer of hearts; He guides whom He will and leads astray whom He will.
Imam Abu Hamid al-Ghazali, The Beginning of Guidance