A placeholder for listing the absurdity of Christianity (‘absurdist’ used in the ‘Camus-Sisyphean’ sense). Note that some of these are not exclusive to Christianity.
(1) The book of Ecclesiastes and the meaningless of things (more an existential root for the absurdity)
(2) Matthew 20:16: So the last will be first, and the first last.
(3) Mark 4:10-12: And when he was alone, those around him with the twelve asked him about the parables. And he said to them, “To you has been given the secret of the kingdom of God, but for those outside everything is in parables, so that
“‘they may indeed see but not perceive,
and may indeed hear but not understand,
lest they should turn and be forgiven.’”
(4) The mystery of the trinity
(5) That God must ‘die’ to save us (see https://www.sermoncentral.com/sermons/seven-great-bible-paradoxes-rodelio-mallari-sermon-on-bible-truth-151576?page=1 for more great examples)
(6) That we must ‘choose’ to believe