When those on the day of Pentecost realized they had slain the sinless, resurrected Son of God, they asked what they should do to be forgiven. Though most modern preachers would tell people to simply “accept Jesus as their personal Savior,” to “pray the sinner’s prayer,” or “ask Jesus to come into their hearts,” that is not what Peter instructed them to do:
“Men and brethren, what shall we do? Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call. And with many other words did he testify and exhort, saying, Save yourselves from this untoward generation. Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls” (Acts 2:38-41).
When they were baptized in water for the forgiveness of their sins, they became saved, and the Lord “added [the saved] to the church” (Acts 2:47; cf. 2:41; 8:36; 10:47, 48). To which church were they added? They were added to the one church Christ promised to build–His church: “upon this rock I will build my church” (Matthew 16:18; cf. Ephesians 1:22, 23; 4:4; Colossians 1:18). That is why we often call it the church of Christ, because it belongs to Him (cf. Romans 16:16). Paul said that Jesus is the Savior of that one body, that one church (Ephesians 5:23).
If Christ is the Savior of the body/church, and one is not added to the church until water baptism, then Christ is not one’s Savior until baptism. This fact is also confirmed by the remainder of the New Testament Scriptures (Matthew 28:19; Mark 16:15, 16; John 3:5; Romans 6:3-5; 16-18; 1 Corinthians 6:11; Galatians 3:26-29; Ephesians 5:25, 26; Colossians 2:11-13; Titus 3:5; Hebrews 10:22; 1 Peter 3:20, 21, etc.).
You may also be interested in reading:
Cornelius Does Not Help “Faith Only” Advocates