"For the priesthood being changed, of necessity there is also a change of the law."
Where does the Bible say that the Law is eternal?
"But if the ministry of death, written and engraved on stones, was glorious, so that the children of Israel could not look steadily at the face of Moses because of the glory of his countenance, which glory was passing away, how will the ministry of the Spirit not be more glorious? For if the ministry of condemnation had glory, the ministry of righteousness exceeds much more in glory. For even what was made glorious had no glory in this respect, because of the glory that excels. For if what is passing away was glorious, what remains is much more glorious."
"For the law of the Spirit of life in Christ Jesus has made me free from the law of sin and death."
A covenant is different from a command. What about this?
Leviticus 24:8 NASB - "Every sabbath day he shall set it in order before the LORD continually; it is an everlasting covenant for the sons of Israel.
And then for example and discussion we have the word perpetual:
Exodus 27:21 NASB - "In the tent of meeting, outside the veil which is before the testimony, Aaron and his sons shall keep it in order from evening to morning before the LORD; it shall be a perpetual statute throughout their generations for the sons of Israel.
Exodus 29:9 NASB - "You shall gird them with sashes, Aaron and his sons, and bind caps on them, and they shall have the priesthood by a perpetual statute. So you shall ordain Aaron and his sons.
Exodus 31:16 NASB - 'So the sons of Israel shall observe the sabbath, to celebrate the sabbath throughout their generations as a perpetual covenant.'
Exodus 40:15 NASB - and you shall anoint them even as you have anointed their father, that they may minister as priests to Me; and their anointing will qualify them for a perpetual priesthood throughout their generations."
I don't have the words Law and eternal in one verse.
A couple of verses with everlasting and law in them are these.
1 Chronicles 16:17 KJV - And hath confirmed the same to Jacob for a law, and to Israel for an everlasting covenant,
Psalm 105:10 KJV - And confirmed the same unto Jacob for a law, and to Israel for an everlasting covenant:
Now Jacob was before the Law (of Moses).