Jesus is called the Great High Priest because “He makes propitiation for the sins of the people” Hebrews 2:17; and He intercedes on our behalf to God (Hebrews 7:25). Jesus is not like the priests who had to offer up sacrifices and offerings daily for himself(priest) and for the people. The sacrifice Jesus made is without an expiration date. He has been perfected forever (Hebrews 7:23-28).
As a result we have gained a High Priest who is able to sympathize with our weakness (Hebrews 4:15), is holy, harmless, undefiled, separate from sinners (Hebrews 7:26).
For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin. Hebrews 4:15
Also there were many priests, because they were prevented by death from continuing. But He, because He continues forever, has an unchangeable priesthood. Therefore He is also able to save to the uttermost those who come to God through Him, since He always lives to make intercession for them. For such a High Priest was fitting for us, who is holy, harmless, undefiled, separate from sinners, and has become higher than the heavens; who does not need daily, as those high priests, to offer up sacrifices, first for His own sins and then for the people’s, for this He did once for all when He offered up Himself. For the law appoints as high priests men who have weakness, but the word of the oath, which came after the law, appoints the Son who has been perfected forever. Hebrews 7:23-28