Irving thematically presents opposing world views displayed through a contrast in the views of the two main characters: the narrator, Johnny Wheelwright, and his best friend, Owen Meany. Owen Meany, by nature, is a character who believes in God and fate. Further, he believes everyone is born with a specific purpose in life. Johnny, on the other hand, as a child, is filled with questions and doubt despite his religious upbringing. The ideas of fate and purpose are particularly difficult for this orphan bastard child to accept, given that for a long time, he does not know the identity of his father, and his mother is killed (by his best friend and a foul baseball) when he is still pretty young.
The majority of the novel presents the conflict of these two very basic ideas through the ongoing and deepening friendship of Owen and Johnny, and does not seem to settle on just one correct answer. Owen alludes to his "fate" throughout the book and eventually dies carrying out what he believes to be his purpose in life (rescuing a group of children in an airport bathroom from a bomber). Between this death, his mother's death, and (at this point) the continued mystery of his father's identity, Johnny could very easily have simply given up on any sort of faith whatsoever.
But he does not.
The opening paragraph of the novel allows the reader to know in advance that despite a long and difficult life journey, Johnny eventually becomes a man of faith and belief in God. Though it is not fully revealed whether his grasp of faith and purpose ever reaches the depth of his friend Owen, he does admit to arriving at a similar conclusion and way of looking at the world when he says (beginning on page 1):
...he is the reason I believe in God; I am a Christian because of Owen Meany...What faith I have I owe to Owen Meany, a boy I grew up with. It is Owen who made me a believer.
Though in comparison to Owen, Johnny may consider his belief to be in the stages of infancy, he does have a grasp of something rather than nothing. In that same passage he admits to having a limited knowledge of Scripture, a conflicting view of the church, and a lack of desire to be "pious." But he is also very clearly at peace with who he is, what he believes, and why. Though he does not present one clear and distinct answer, Irving suggests that faith (in some capacity) is a "worked out way of looking at the world." But because the main characters never fully agree with one another, Irving also suggests that concluding on one world view is ultimately a personal and individual decision.