"With regards to gratitude, it perpetuates the blessings and increases them to an unimaginable extent. Those who are neglectful in this are considers to be 'kafirs', i.e., deniers of truth and deniers of divine favours. God says (in the Holy Quran), "If you show gratitude to me I shall increase my blessings on you. If you become 'kafirs', i.e. if you deny my favours then my punishment is very severe." (Surah 14, Ayat 7). The Prophet says "If one does you a good turn you must reciprocal to him. If you cannot do so then thank him. If you fail to do so you become 'kafir', i.e., the denier of his favours." God does not like that we should be ungrateful to Him for the favours that He has done to us. He does not approve of ingratitude even from man to man for the good turn that one may do to another. He says, "Be grateful to me and to your parents. You have to return to me." (Surah 31, Ayat 14).
The Prophet says. "On the day of judgement, God will say to someone of the ungrateful persons 'such and such a man did you a good turn but you did not thank him and denied his favour'. The man will say in reply, 'I thought that you were the source of the good turn he did to me and I thanked you for it. God will say, 'How could you thank me when you did not thank the person I had made a medium of doing you a good turn?"
To sum up, if to thank our parents for bringing us up and to thank those men who do us a favour, is a duty enjoined on us by God and want of it amounts to 'kufr', then it needs no imagination to realize the magnitude of the importance of our thanks to the Imams whose favours on us are beyond our calculations.
Let us make a short survey of their favours on us. We were ignorant of everything and were spiritually dead. They brought us back to life and showed us the path of wisdom. We were blind, they gave us the eyes to see for ourselves what is right and what is wrong. We were groping in the dark, they showed us the light. We had lost the track, they showed us the way to salvation. We were lacking in knowledge, they gave us knowledge. We were falling in hell-fire, they picked us up and put us in the middle of righteous. In short, they gave done us the favours which we cannot count. They have given us all that is good in this world and the world to come."