Actually, I'm not a Protestant either. I fashion my beliefs according to the First Century Church of the Apostles. This means that I observe the Sabbath as well as the seven Holy Feast days as expressed in [Leviticus 23].
The understanding of struggling with sin, even after Baptism, was the understanding of both St. Ambrose and St. Augustine and it is obvious that St.Paul is noting that he still struggles with sin “What I do, I do not understand. For I do not do what I want, but do what I hate” (c.f. Romans 7:16). St. Paul makes similar statements in Romans 7:20.
We all struggle with sin and will continue to struggle with sin as long as we are flesh and blood.....and until we are born again of the spirit. I liken the begetting process (baptism) as a sperm fertilizing the egg. Then the process of gestation begins....the growing in the word and the commitment and service to Our Lord. After the gestation is over the birth occurs and at that point the "born again" individual will be like Our Lord.....immortal and composed of spirit. And as the Apostle John mentions.....unable to sin.
The Catholic Church affirms the teaching in the Sacred Scriptures which clearly teach the doctrine that Baptism is the normative means through which God gives humanity Grace, which saves us. Numerous passages support this doctrinal point (e.g., see Acts 2:38, 22:16; Rom. 6:1–4; 1 Cor. 6:11, 12:13; Gal. 3:26–27; Eph. 5:25-27; Col. 2:11–12; Titus 3:5; 1 Pet. 3:18–22). These passages all point to a being baptized into Christ’s passion, death and resurrection, and thus a communion with God.
The Catechism of the Catholic Church, in paragraph 628, summarizes this point nicely:
“Baptism, the original and full sign of which is immersion, efficaciously signifies the descent into the tomb by the Christian who dies to sin with Christ in order to live a new life. “We were buried therefore with him by baptism into death, so that as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life (c.f. Rom 6:4).”
Here is a fuller explanation on the Catholic understanding of Baptism
http://www.usccb.org/catechism/text/pt2sect2.shtml#art1
In addition, the constant witness of the early Church Fathers stressed Baptism [quotes taken from Jurgens Faith of our Fathers]
St. Ignatius of Antioch writes:
“Let none of you turn deserter. Let your baptism be your armor; your faith, your helmet; your love, your spear; your patient endurance, your panoply” (Letter to Polycarp 6 [A.D. 110]).
St. Justin Martyr writes
“Whoever are convinced and believe that what they are taught and told by us is the truth, and professes to be able to live accordingly, are instructed to pray and to beseech God in fasting for the remission of their former sins, while we pray and fast with them. Then they are led by us to a place where there is water, and they are reborn in the same kind of rebirth in which we ourselves were reborn: ‘In the name of God, the Lord and Father of all, and of our Savior Jesus Christ, and of the Holy Spirit,’ they receive the washing of water. For Christ said, ‘Unless you be reborn, you shall not enter the kingdom of heaven’” (First Apology 61:14–17 [A.D. 151]).
St. Cyril of Jerusalem writes:
“If any man does not receive baptism, he does not have salvation. The only exception is the martyrs, who, even without water, will receive baptism, for the Savior calls martyrdom a baptism [Mark 10:38]. . . . Bearing your sins, you go down into the water; but the calling down of grace seals your soul and does not permit that you afterwards be swallowed up by the fearsome dragon. You go down dead in your sins, and you come up made alive in righteousness” (Catechetical Lectures 3:10, 12 [A.D. 350]).
St. Ambrose of Milan writes:
“The Lord was baptized, not to be cleansed himself but to cleanse the waters, so that those waters, cleansed by the flesh of Christ which knew no sin, might have the power of baptism. Whoever comes, therefore, to the washing of Christ lays aside his sins” (Commentary on Luke 2:83 [A.D. 389]).
St. Augustine writes:
“It is an excellent thing that the Punic [North African] Christians call baptism salvation and the sacrament of Christ’s body nothing else than life. Whence does this derive, except from an ancient and, as I suppose, apostolic tradition, by which the churches of Christ hold inherently that without baptism and participation at the table of the Lord it is impossible for any man to attain either to the kingdom of God or to salvation and life eternal? This is the witness of Scripture too” (Forgiveness and the Just Deserts of Sin, and the Baptism of Infants 1:24:34 [A.D. 412]).
“The sacrament of baptism is most assuredly the sacrament of regeneration.....by the Sacrament of Baptism, conformed to the death of Christ, they are also freed from the serpent’s venomous bite” (Also from Forgiveness and the Just Deserts of Sin and the Baptism of Infants, 2:27:43).
“We say that Baptism grants forgiveness of all sins” (Against Two Letters of the Pelagians [A.D. 420]).
“This is the meaning of the great sacrament of baptism, which is celebrated among us: all who attain to this grace die thereby to sin—as he himself [Jesus] is said to have died to sin because he died in the flesh (that is, ‘in the likeness of sin’)—and they are thereby alive by being reborn in the baptismal font, just as he rose again from the sepulcher. This is the case no matter what the age of the body. For whether it be a newborn infant or a decrepit old man—since no one should be barred from baptism—just so, there is no one who does not die to sin in baptism. Infants die to original sin only; adults, to all those sins which they have added, through their evil living, to the burden they brought with them at birth” (Handbook on Faith, Hope, and Love 13[41] [A.D. 421]).
So it is the Apostolic Tradition and thus orthodox Christian doctrine that Baptism is the “normative means” by which God gives us grace as affirmed by both the Scriptures and Tradition (i.e. Teachings of the Patristic Fathers).
Regards