You misunderstand those verses about their no longer being a sacrifice for sin. This is not for or about New Covenant Christians, this verse pertains to the Jewish believers in Christ who were coming from the Old Covenant into the New Covenant.
Under the Old Covenant, the Levitical priesthood made sacrifices for sin. Temporary atonement for sin UNTIL the Messiah came. What they are being told is that there is no longer temporary atonement for sin through the Levitical priesthood and that any and ALL atonement for sin is now through Christ.
I have included much of the chapter that contains this verse so you can see the context. This is often a verse that is misunderstood.
Hebrews 10:1-25
1For the Law, since it has
only a shadow of the good things to come
and not the very form of things, can never,
by the same sacrifices which they offer continually year by year, make perfect those who draw near.
2Otherwise, would they not have ceased to be offered, because the worshipers, having once been cleansed, would no longer have had consciousness of sins?
3But
in those sacrifices there is a reminder of sins year by year. 4For it is impossible for the blood of bulls and goats to take away sins.
5Therefore, when He comes into the world, He says,
“SACRIFICE AND OFFERING YOU HAVE NOT DESIRED,
BUT A BODY YOU HAVE PREPARED FOR ME;
6IN WHOLE BURNT OFFERINGS AND
sacrifices FOR SIN YOU HAVE TAKEN NO PLEASURE.
7“THEN I SAID, ‘BEHOLD, I HAVE COME
(IN THE SCROLL OF THE BOOK IT IS WRITTEN OF ME)
TO DO YOUR WILL, O GOD.’”
8After saying above, “
SACRIFICES AND OFFERINGS AND WHOLE BURNT OFFERINGS AND
sacrifices FOR SIN YOU HAVE NOT DESIRED, NOR HAVE YOU TAKEN PLEASURE
in them” (which are offered according to the Law),
9then He said, “BEHOLD, I HAVE COME TO DO YOUR WILL.” He takes away the first in order to establish the second.
10By this will we have been sanctified through the offering of the body of Jesus Christ once for all.
11Every
priest stands daily ministering and offering time after time the same sacrifices, which can never take away sins;
12but He, having offered one sacrifice for sins for all time, SAT DOWN AT THE RIGHT HAND OF GOD,
13waiting from that time onward UNTIL HIS ENEMIES BE MADE A FOOTSTOOL FOR HIS FEET.
14For by one offering He has perfected for all time those who are sanctified.
15And the Holy Spirit also testifies to us; for after saying,
16“THIS IS THE COVENANT THAT I WILL MAKE WITH THEM
AFTER THOSE DAYS, SAYS THE LORD:
I WILL PUT MY LAWS UPON THEIR HEART,
AND ON THEIR MIND I WILL WRITE THEM,”
He then says,
17“AND THEIR SINS AND THEIR LAWLESS DEEDS
I WILL REMEMBER NO MORE.”
18 Now where there is forgiveness of these things, there is no longer any offering for sin.
A New and Living Way
19Therefore, brethren, since we have confidence to enter the holy place by the blood of Jesus,
20by a new and living way which He inaugurated for us through the veil, that is, His flesh,
21and since
we have a great priest over the house of God,
22let us draw near with a sincere heart in full assurance of faith, having our hearts sprinkled
clean from an evil conscience and our bodies washed with pure water.
23Let us hold fast the confession of our hope without wavering, for He who promised is faithful;
24and let us consider how to stimulate one another to love and good deeds,
25not forsaking our own assembling together, as is the habit of some, but encouraging
one another; and all the more as you see the day drawing near.
