Sufyaan ibn `Abdillaah radhiallahu `anhu said: "O Messenger of Allah, tell me something about Islaam, which I cannot ask anyone else besides you." He said: "Say: 'I believe in Allah' and then be steadfast (upon that)." [Saheeh Muslim (38)]
The hadeeth is proof that the servant is obligated, after having eemaan in Allah, to persevere and be steadfast upon obeying Him by performing the obligatory acts and avoiding the prohibited ones. This is achieved by following the Straight Path, which is the firm Religion without drifting away from it, to the right or to the left.
This lecture covers the reasons a person sways back and forth, as well as ways to Remain steadfast upon Islam.