By the washing of regeneration I have no doubt that he alludes, at least, to baptism, and even I will not object to have this passage expounded as relating to baptism; not that salvation is contained in the outward symbol of water, but because baptism tells to us the salvation obtained by Christ. Paul treats of the exhibition of the grace of God, which, we have said, has been made by faith. Since therefore a part of revelation consists in baptism, that is, so far as it is intended to confirm our faith, he properly makes mention of it. Besides, baptism — being the entrance into the Church and the symbol of our ingrafting into Christ — is here appropriately introduced by Paul, when he intends to shew in what manner the grace of God appeared to us; so that the strain of the passage runs thus: — “God hath saved us by his mercy, the symbol and pledge of which he gave in baptism, by admitting us into his Church, and ingrafting us into the body of his Son.”
Now the Apostles are wont to draw an argument from the Sacraments, to prove that which is there exhibited under a figure, because it ought to be held by believers as a settled principle, that God does not sport with us by unmeaning figures, but inwardly accomplishes by his power what he exhibits by the outward sign; and therefore, baptism is fitly and truly said to be “the washing of regeneration.” The efficacy and use of the sacraments will be properly understood by him who shall connect the sign and the thing signified, in such a manner as not to make the sign unmeaning and inefficacious, and who nevertheless shall not, for the sake of adorning the sign, take away from the Holy Spirit what belongs to him. Although by baptism wicked men are neither washed nor renewed, yet it retains that power, so far as relates to God, because, although they reject the grace of God, still it is offered to them.
But here Paul addresses believers, in whom baptism is always efficacious, and in whom, therefore, it is properly connected with its truth and efficacy. But by this mode of expression we are reminded that, if we do not wish to annihilate holy baptism, we must prove its efficacy by “newness of life.” (Romans 6:4.)
And of the renewing of the Holy Spirit
Though he mentioned the sign, that he might exhibit to our view the grace of God, yet, that we may not fix our whole attention on the sign, he immediately sends us to the Spirit, that we may know that we are washed by his power, and not by water, agreeably to what is said, —
“I will sprinkle on you clean waters, even my Spirit.” (Ezekiel 36:25, 27.)
And indeed, the words of Paul agree so completely with the words of the Prophet, that it appears clearly that both of them say the same thing. For this reason I said at the commencement, that Paul, while he speaks directly about the Holy Spirit, at the same time alludes to baptism. It is therefore the Spirit of God who regenerates us, and makes us new creatures; but because his grace is invisible and hidden, a visible symbol of it is beheld in baptism. Some read the word “renewing,” in the accusative case, thus: — “through the washing of regeneration and (through) the renewing of the Holy Spirit.”, But the other reading — “through the washing of regeneration and of the renewing of the Holy Spirit” — is, in my opinion, preferable.
Commentary on Timothy, Titus, Philemon | Christian Classics Ethereal Library