In the Old Testament God used animals sacarefully sacrificed on the alter in the temple of God to cover the sins of people but that system was not good enough. Jesus completely fulfilled the needed sin sacrifice when with a sinless life He died on the cross  for all humanity– past, present and future.

Hebrews 10:

12 But our High Priest offered himself to God as a single sacrifice for sins, good for all time. Then he sat down in the place of honor at God’s right hand. 13 There he waits until his enemies are humbled and made a footstool under his feet. 14 For by that one offering he forever made perfect those who are being made holy.

15 And the Holy Spirit also testifies that this is so. For he says,

16 “This is the new covenant I will make
with my people on that day,[a] says the Lord:
I will put my laws in their hearts,
and I will write them on their minds.”
17 Then he says,

“I will never again remember
their sins and lawless deeds.”