'Truth of the Gospel' in the Bible

To whom we gave place by subjection, no, not for an hour; that the truth of the gospel might continue with you.

But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?

For the hope which is laid up for you in heaven, whereof ye heard before in the word of the truth of the gospel;

I have not written to you, as to people unacquainted with the truth of the gospel: but as to such who know it, and know that it cannot give rise to any imposture.