John Calvin Commentary Titus 1:4

"to Titus, my true child after a common faith: Grace and peace from God the Father and Christ Jesus our Saviour." — Titus 1:4 (ASV)

To Titus, my own son, according to the common faith. Therefore, it is clear in what sense a minister of the Word is said to spiritually beget those whom he brings to the obedience of Christ; that is, in such a way that he himself is also begotten. Paul declares himself to be the father of Titus regarding his faith, but immediately adds that this faith is common to both, so that both of them equally have the same Father in heaven.

Thus, God does not diminish His own prerogative when He declares certain individuals to be spiritual fathers alongside Himself, through whose ministry He regenerates whomever He chooses; for by themselves they do nothing, but only by the efficacy of the Spirit. As for the rest of the verse, its explanation will be found in the Commentaries on the former Epistles, and especially on the First Epistle to Timothy.