'Truth of the Gospel' in the Bible

to whom not even for an hour did we yield by the required subjection, that the truth of the gospel might still remain with you.

But when I saw that they were not walking uprightly according to the truth of the gospel, I said to Cephas in the presence of all, If thou, being a Jew, livest after the manner of gentiles, and not that of the Jews, how is it that thou compellest the gentiles to keep the customs of the Jews?

on account of the hope which is laid up for you in the heavens, of which ye heard before in the word of the truth of the gospel,