Jesus paid for sins committed under the old covenant.
And for this cause he is the mediator of the new covenant, that by means of death, for the redemption of the transgressions that were under the first covenant, they which are called might receive the promise of eternal inheritance. Hebrews 9:15
Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; Romans 3:25
But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins. 2 Peter 1:9
The word translated
sins in Romans 3:25 and 2 Peter 1:9 is not the normal word used for sins (αμαρτια, hamartia). The word is ἁμάρτημα (harmatema) which is αμαρτια with the -
ma suffix, which means
effect. So in effect, ἁμάρτημα (harmatema) means
sin effect, or
consequence of sin. It is rarely used in the NT (5x), but it is used quite a few times in the LXX. Sin effect is the only meaning that makes sense where is it used in verses like Isaiah 40:2 and Deuteronomy 19:15.
So as I read Romans 3:25 and 2 Peter 1:9, they are saying that those under the old covenant were freed from the consequences of sin under the old covenant, i.e. death or being cut off from the covenant.
Christ's death enacted a new covenant, under which old covenant law with its penalties do not apply. When we sin now, we sin against the light, not against old covenant law.
What we have now is a covenant that guarantees the forgiveness of sins. As we abide in Christ, all sin is forgiven. If we sin, we need to acknowledge such and be cleansed. As it is written
But if we walk in the light as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin. 1 John 1:7
The blood cleanses (present tense), not cleansed (past tense). So IMO anyone who thinks their past, present and future sins were forgiven (cleansed) at the cross is delusional. Sin can't be forgiven before it's committed. Cleansing of sin is in the here-and-now.