HIGH PRIEST IN THE BIBLE

In the days of His flesh,
when He offered up prayers and supplications
with strong crying and tears to God,
who was able to save Him from death,
and was heard that He feared;
though He were God's Son,
still, He learned obedience by the things that He suffered;
and being made perfect,
Jesus became the author of eternal salvation
to all them that obey Him;
called of God an high priest after the order of Melchisedec.
Of whom we have many things to say,
and hard to be expressed,
because you are slow of understanding.

The Hebrews were difficult to teach. They were probably so attached to the old ways of thinking from being raised with unmovable dedication to the Old Testament, that they had a hard time holding on to the understanding of the Gospel of Christ. They probably slipped back into their old habits frequently, so Paul encourages them to change their habits by practicing their new ones.

For the time when you ought to be teachers,
you need someone to teach you again
what the first principles are of the oracles (messages, sayings, TRUTH) of God;
and seem again to have need of milk (like babies),
and not of strong meat.
For every one that uses milk
is unskillful in the word of righteousness:
for he is a babe.
But strong meat is for those that are mature,
that is, those who by practicing have their senses trained
to tell the difference between good and evil.