Titus 3:5

Paul rules something out before he says anything positive, and the order is deliberate.

Not by works of righteousness, which we did ourselves. Note that he does not say we had no works of righteousness. He says they were not the basis. That is a finer distinction and a more uncomfortable one. It concedes the works may exist and denies them any load-bearing role.

Anyone who has tried to hold a position of standing before God knows why the denial has to be that firm. Works make excellent evidence and terrible foundations. They are always partial, always mixed in motive, and always subject to a bad month.

According to his mercy is what replaces them, and mercy is by definition not earned. If it were owed it would be justice, which is a different transaction with a different name.

Then two images for what happened. Washing suggests something removed, the old state cleaned off. Renewing suggests something made, a new state produced. Removal and production — you need both, because a clean version of the old thing is still the old thing.

And the agent named in both is the Holy Spirit. Paul has now removed human effort from the basis, from the mechanism, and from the maintenance. What is left for the reader to do is in the next verse, and it is to believe it.