In verses 5-6, the author quotes Psalm 2 and Psalm 110 to show that Someone greater—the Most High—commanded things regarding Jesus, including His role as High Priest. That shows that Jesus did not glorify Himself to step into that role—it was presented to Him. Remember our contrast with Helel, who did glorify and exalt himself in his determination to ascend to a position to which he had not been appointed.
Along those lines, James says that self-seeking is an aspect of demonic wisdom (James 3:14-16), meaning it is a skill the unclean spirits have and use, as exemplified by Satan. It is part of his spirit, and it shows up in selfish ambition, which is one of the works of the flesh. But Christ’s approach is completely opposite. He waited for the Father to raise Him up.
