- I believe this verse was said after Christ arose.
Yes, this was.
The old (Mosiac) covenant
has been made ancient, obsolete (Heb 8:13).
Your setting the Scriptures against themselves is
ipso facto proof you do not understand them correctly,
for the word of God does not contradict itself.
4For if he were on earth, he should not be a priest,
[seeing that there are priests] that offer gifts according to the law:
Yes, he would not be a priest in the order of Aaron because he was not of the tribe of Levi.
However, he is a priest in the order of Melchizedek, and its eternal High Priest.
There are not two orders of priests, and the order of Melchizedek is unending, eternal.
There is no other priesthood.
The change in the priesthood (Heb 7:12) required a change in the
law (Heb 7:12)
given to the people (Heb 7:11),
which was set aside because it was weak and useless to make perfect, and
God's people are no longer under the law (1Co 9:20-21),
the old (Mosaic) covenant
has been made ancient/obsolete (Heb 8:13),
and God's one people are under the new covenant (Lk 22:20)
whose laws are two (Mt 22:37-39) and
obedience to which accomplishes, fulfills all God's law (Mt 22:40; Ro 13:8, 9, 10; Jas 2:8).
The old (Mosaic) covenant, the Levitical priesthood, and Mosaic regulations have all been set aside
and replaced with the new covenant (Lk 22:20), the eternal priesthood in the order of Melchizedek and
the new covenant laws of Mt 22:37-39, obedience to which is obedience to all of God's laws (Mt 22:40;
Ro 13:8, 9, 10).