There is, on the one hand, the abrogation of an earlier commandment because it was weak and ineffectual
(for the law made nothing perfect); there is, on the other hand, the introduction of a better hope, through which we approach God.
This was confirmed with an oath; for others who became priests took their office without an oath,
but this one became a priest with an oath, because of the one who said to him, "The Lord has sworn and will not change his mind, "You are a priest forever' "—
accordingly Jesus has also become the guarantee of a better covenant.
Furthermore, the former priests were many in number, because they were prevented by death from continuing in office;
but he holds his priesthood permanently, because he continues forever.
Consequently he is able for all time to save those who approach God through him, since he always lives to make intercession for them.
References for Hebrews 7:25
For it was fitting that we should have such a high priest, holy, blameless, undefiled, separated from sinners, and exalted above the heavens.
Unlike the other high priests, he has no need to offer sacrifices day after day, first for his own sins, and then for those of the people; this he did once for all when he offered himself.
References for Hebrews 7:27
For the law appoints as high priests those who are subject to weakness, but the word of the oath, which came later than the law, appoints a Son who has been made perfect forever.