They did both but it seems one is of more infinite value that in your mind God could not have allowed the world to exist without, that is a text of almost Quranic like properties. I don’t see why that is the case however, why there absolutely needs to be a Bible if the truth can be spread within the community of the faithful, as it was long before there was a bible. The only reason would be if the contents of the orally presented Gospel are insufficient and perhaps when presented by certain people it is, but not by trained or ordained people, like the apostles. Surely they had the fullness of the faith and passed it down in the manner they saw fit. If the Gospel could be spread first among the apostles by their speaking and the apostles themselves didn’t seem to consider writing the bible one of their main tasks (rather their main task seems to have been establishing church communities), why think the bible is so necessary?