Like PiousTemplar, I’m willing to let the experts correct me, but I’ll hazard a guess… well, a couple guesses.
First, it might be that they
did ask, but the Gospel writers didn’t put it in the Gospels because they knew that the “nuts and bolts” of what “the Church” or “My Church” meant (that’s Jesus’ “My” from Matt 16:18, of course) was being passed on orally. We have to remember that in the first several centuries the Bible was almost exclusively a liturgical document. The Gospels especially were written specifically to be read aloud
in Mass, so an explanitory aside about what the Church is would be a bit extraneous when the people hearing it read to them were experiencing the very core of Church life even as they heard it: they were celebrating the Divine Liturgy.
Second, it could also be that they didn’t ask for a very similar reason. The word “church” (or “ekklesia” in Greek) means something like “an assemply of those called.” And the biblical concept of calling is of course a call to be holy, to be set apart for God. Now, the People of God in the Old Testament, the Israelites/Jews, were very familiar with being called together as people set apart for God, and when they came together, they heard the Word of God - the Torah - and then they heard the interpretation of the Word, and then, if they were in the Temple in Jerusalem, the priests would offer sacrifice and then they would eat and/or drink the sacrifice. So, to the Jews, the concept of a gathereing of the called was, again, the familiar idea of the People of God called together to celebrate the Liturgy as set down for them to do by God.
I don’t have sources, and I don’t know the ins and outs of Jewish worship - but I do know that the Mass is the fullfillment, the perfection and completion, of the worship of the Old Covenant, and the Church is the fulfillment of the OT concept of the People of God. So, for the first audiences of the Bible, while the idea of the Church had to be expanded and fleshed out so that they could understand that it now means that the People of God truly are the Body of Christ - all of us together being many members of the One Body, as Paul says - the primary, basic idea was nevertheless probably familiar enough to them that they wouldn’t have been completely confused by it. … I think.
