Thank you for asking a question on www.thisisyourbible.com
The difference is that only those baptised into Christ can have their sins forgiven. Those outside the body of Christ will die in their sins.
John 8:24 I said therefore unto you, that ye shall die in your sins: for if ye believe not that I am he, ye shall die in your sins.
Acts 2:38 Then Peter said to them, "Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins...
Acts 10:43 "To Him all the prophets witness that, through His name, whoever believes in Him will receive remission of sins."
In Acts 10 it is assumed that baptism will follow belief. Only by baptism can we become part of the body of Christ. Belief without baptism is in vain.
Mark 16:16 "He who believes and is baptized will be saved;
At baptism all our previous sins are washed away and we begin a new life in Christ.
Acts 22:16 ‘And now why are you waiting? Arise and be baptized, and wash away your sins, calling on the name of the Lord.’
After baptism, if we sin through weakness as members of the body of Christ we can be forgiven if we confess and ask for forgiveness, as John explains:
1 John 1:7 But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin. 8 If we say that we have no sin, we deceive ourselves, and the truth is not in us. 9 If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.
If on the other hand we continue in sin wilfully, we will be rejected when we are judged.
Hebrews 10:26 For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries. 28 Anyone who has rejected Moses’ law dies without mercy on the testimony of two or three witnesses. 29 Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace? 30 For we know Him who said, "Vengeance is Mine, I will repay," says the Lord. And again, "The LORD will judge His people." 31 It is a fearful thing to fall into the hands of the living God.