To take something as truth without question

You'd better not take for Gospel truth everything you read on newspapers

Non devi prendere per Vangelo tutto quello che leggi sui giornali

Mark is really gullible: he takes as Gospel truth everything he hears on TV

Marco è proprio un credulone: prende per oro colato tutto quello che sente alla televisione

I know he's a world-class expert on this matter and whatever he says on the subject is Gospel for me

So che è un esperto di livello mondiale in materia e qualsiasi cosa dica al riguardo, per me è Vangelo

This expression refers to the first four books of the New Testament, which are the Christian Gospels. Since the Bible is considered to be the word of God, it follows that a true believer must accept the Gospel as absolute truth