'Mystery' in the Bible

making known to us the mystery of his will, according to his good pleasure which he purposed in him

how that by revelation the mystery was made known to me, as I wrote before in few words,

by which, when you read, you can perceive my understanding in the mystery of Christ;

and to make all men see what is the administration of the mystery which for ages has been hidden in God, who created all things through Jesus Christ;

This mystery is great, but I speak concerning Christ and of the assembly.

on my behalf, that utterance may be given to me in opening my mouth, to make known with boldness the mystery of the Good News,