Jesus' sacrifice perfects those who are sanctified in Him. Why is it so important for believers to require no further offering for sin?

The New and Living Way | Episode 25 | Hebrews 10:5-18

Wherefore when he cometh into the world, he saith, "Sacrifice and offering thou wouldest not, But a body didst thou prepare for me; In whole burnt offerings and sacrifices for sin thou hadst no pleasure: Then said I, Lo, I am come (In the roll of the book it is written of me) To do thy will, O God."

Saying above, "Sacrifices and offerings and whole burnt offerings and sacrifices for sin thou wouldest not, neither hadst pleasure therein" (the which are offered according to the law), then hath he said, "Lo, I am come to do thy will." He taketh away the first, that he may establish the second.

By which will we have been sanctified through the offering of the body of Jesus Christ once for all. And every priest indeed standeth day by day ministering and offering oftentimes the same sacrifices, the which can never take away sins: but he, when he had offered one sacrifice for sins for ever, sat down on the right hand of God; henceforth expecting till his enemies be made the footstool of his feet. For by one offering he hath perfected for ever them that are sanctified.

And the Holy Spirit also beareth witness to us; for after he hath said, "This is the covenant that I will make with them After those days, saith the Lord: I will put my laws on their heart, And upon their mind also will I write them;" then saith he, "And their sins and their iniquities will I remember no more."

Now where remission of these is, there is no more offering for sin.