(painting by Annibale Carracci "Baptism of Jesus" 1584)
Our Baptism abides forever. Even though someone should fall from Baptism and sin, still we always have access to it. So we may subdue the old man again. But we do not need to be sprinkled with water again...Even if we were put under the water a hundred times, it would still be only one Baptism, even though the work and sign continue and remain. Repentance, therefore, is nothing other than a return and approach to Baptism. We repeat and do what we began before, but abandoned.
I say this lest we fall into the opinion in which we were stuck for a long time. We were imagining that our Baptism is something past, we we can no longer use after we have fallen into sin. The reason for this is that Baptism is regarded as only based on the outward act once performed and completed. This arose from the fact that St. Jerome wrote that "repentance is the second plank by which we must swim forth and cross over the water after the ship is broken, on which we step and are carried across when we come into the Christian Church." By this teaching Baptism's use has been abolished so that it can no longer profit us. Therefore, Jerome's statement is not correct, or at any rate is not rightly understood. For the ship of Baptism never breaks, because...It is God's ordinance and not our work (1 Peter 3:20-22). But it does happen, indeed, that we slip and fall out of the ship. Yet if anyone falls out, let him see to it that he swims up and clings to the ship until he comes into it again and lives in it, as he had done before.
In this way one sees what a great, excellent thing Baptism is. It deliver us from the devil's jaws and makes us God's own. It suppresses and takes away sin and then daily strengthens the new man. It is working and always continues working until we pass from this estate of misery to eternal glory.
Large Catechism IV 77-83