Many Protestants (unless you speak of Lutherans and Anglicans) limit salvation to a once and for all thing. They go against the Bible which says we have been saved (rf. Ephesians 2:8), are being saved (rf. Philippians 2:12), and will be saved (rf. 1 Corinthians 13:5). Salvation is a work in progress and we don’t receive its fruits unless we persevere (rf. Matthew 24:13, Hebrews 6:11).
Our salvation does not end at the baptismal font. This is the flaw of Baptists, Calvinists and other Protestant groups that reject sanctifying grace.
Then there’s the frequent reception of Holy Communion, the Body and Blood of Christ, which shows His Blood cleanses us in actual time. Jesus Christ “has freed us from our sins by his blood” (cf. Revelation 1:5), cleanses us of our sins (rf. 1 John 1:7), and will “cleanse our consciences from dead works” (cf. Hebrews 9:14). The Eucharist is the remedy to sin as many Church Fathers such as Saint Ignatius of Antioch wrote (rf. Ephesians 20:3).
There are many great prayers for sanctifying grace. One of them is the prayer before the crucifix.
Look down upon me, good and gentle Jesus, while before Your face I humbly kneel. And with burning affection I pray and beg You to fix deep in my heart lively sentiments of faith, hope and charity, true contrition for my sins, and a firm purpose of amendment. I contemplate with great love and pity Your five most precious wounds, pondering over them within me, while I call to mind the words which David the prophet said concerning You, my Jesus: They have pierced my hands and my feet; they have numbered all my bones.