The inclusion of a discussion on 3:36 is based primarily on three reasons: (1) the relationship between believing and obedience has been controversial; (2) the relationship is significant for understanding believing; and (3) the lack of attention given to this verse in relationship to this discussion.
The primary purpose of this verse is twofold: (1) unbelief is shown by disobedience; and (2) a contrast in the results of each. The verb apeitheo is in an antonymous relationship to pisteuo. Obedience is presented as a natural result of one who believes. Therefore, the Evangelist’s portrayal of people’s belief can be known by their actions of obedience or disobedience to Jesus. Part of our understanding of repentance relates to this: one aspect of repentance is the changing of one’s actions to line up with God’s Word. This is what obedience is, also. Therefore, while obedience and repentance are not synonyms, nor nearly synonymous, obedience in 3:36 is a result of belief and it is also a result of repentance.
Similarly, Riddlebarger (“Faith,” 104) says that “one who has exercised faith in Christ, and is united to Christ by that faith, will repent and will struggle to obey and yield. But these things are not conditions for nor component parts of faith itself. They are fruits of saving faith. They are the inevitable activity of the new nature.”