Thomas in John’s gospel has often been understood as the prototypical doubter based on Jn 20.27. Jesus’ words are taken as condemning a failure of intellectual belief, despite the shift in 20.27 from the frequent use of πιστεύω to the adjective πιστός. Yet the use of πιστός in other texts denotes faithfulness and often the actions which display faithfulness. The prominent theme of witness in Jn 20, along with contrasts to Synoptic accounts of post-resurrection doubt, point towards Thomas’s failure as a failure to take up Jesus’ commission and become a faithful witness. This is confirmed by Thomas’s response to Jesus, where he becomes an active witness to Jesus as God (20.28).

Matthew uses ὀλιγόπιστος to critique inadequate faith from the disciples, adapting already linked Markan pericopes to create a set with a distinct rhetorical function. For the Gospel audience, these function together to call people to the sort of wholehearted trust exemplified in the first use of the term (6,25–34), while developing this ideal in a christological direction. Linguistic studies on the role of the vocative highlight how ὀλιγόπιστος is used to effect this goal, as it serves to recharacterize the disciples, drawing attention to the narrative frame, and emphasising the imperative force of Jesus’ rhetorical questions.

The Gospel of John seeks to evoke belief, the kind of belief that leads to eternal life (20:31). Yet the language of belief is used to challenge the reader, as in 2:23-25 there are believers whose faith falls short of the belief that leads to life. This account confronts a reader unprepared for the appearance of inadequate faith. In confronting the reader, the scene serves a rhetorical function to provoke the reader to question why this faith falls short, and what genuine belief entails. This pattern is repeated in a series of episodes (6:60-71; 8:30-31; 15:1-6) where characters are described in terms of faith and commitment, and yet in each case the narrative conveys that their faith-response is inadequate. These episodes contribute to a rhetorical strategy whereby readers are continually challenged to understand the nature of genuine belief, in order that they might take on such genuine belief themselves.

The question of who truly believes according to John's Gospel can be unclear, complicated by characters who display contradictory evidence, both portrayed positively yet also reflecting imperfections. A solution to the confusion lies in attending to the overt narration of the Gospel, which creates a distinction between events within the story and the presentation to the reader. Positive expressions of faith within the story can be identified as 'acceptable belief', involving commitment to Jesus but with a limited understanding of his identity and mission. Only after the cross is 'genuine belief', (which includes greater understanding), possible.

Like the Gospel of the same name, the First Letter of John uses the language of faith (πιστεύω κτλ.) extensively. The letter is aimed at encouraging faith (3:23). A key expression within the encouragement of faith is the reference to “our faith” that overcomes the world (5:4). This faith is often understood in primarily cognitive terms, arguing that correct propositional belief overcomes the world. While this reflects an important component of the language of faith in 1 John, it misses another significant aspect. The language of faith within the letter is not only geared toward a correct cognitive response, for the language of faith also contributes to exhorting the audience to right action. The expression ἡ πίστις ἡμῶν (5:4) functions to sum up both the call to right cognitive belief and right action, for it is enduring in both that overcomes the world.