love as the spirit and essence of religion
From what we have been told from hadith, the spirit and essence of religion is nothing but love. ~Burayd al-`Ijli~ said: "I was in the presence of ~Imam al-Baqir~ (as), and there was a traveller from ~Khurasan~ who had traversed that long journey on foot. He had the honour of meeting the Imam. His feet, which were showing through his shoes, were cut, and he had taken his shoes off. He said: "By God, the only thing that brought me from whence I have come is love of you, the ~Household~ (of the Prophet)." The Imam said: "By God, if a stone loved us, God would unite it with us, and join it to us. Is the religion other than love?" [Safinatu 'l-bihar, vol.l, p.201 -under Hubb].
A man said to ~Imam as-Sadiq~ (as): "We have named our children after you and your fathers; will this action be of any benefit to us?" He said: "Yes, by God; is the religion other than love?" Then he gave the verse If you love Allah, follow me, and Allah will love you as evidence. [p.662 -under Sama].
Basically, it is love which brings obedience: the lover does not have the power to refuse the wishes of the one he loves. We have seen this with our own eyes when a youth who was in love left everything when faced with his loved one, his beloved, and sacrificed everything for her.
The obedience and worship of God is in proportion to the love which man has for God, as Imam as-Sadiq (as) said: "Disobey God and show that you love Him; by my life, that is something amazing. If your love were true, you would have obeyed Him, for the lover is submissive before the one whom he loves."
Sources :
attraction and repulsion of Imam Ali p.b.u.h- pages: 61to63