Hebrews 5

He proves now that Christ is a Priest. The natural effort of every one who has to do with ministry is to put himself as a priest between God and man. "Infirmity" is the point in this passage. The Lord is not presented as the "faithful High Priest," as in another place; here it is to offer to God, and as learning obedience. We are shown the dignity of His person, as well as His being appointed Priest. It is interesting to notice that He took the place of a thoroughly dependent man: " He was heard in that he feared." It was not as a priest; but afterward he was appointed priest-" priest forever after the order of Melchisedec."
Verses 13, 14. You cannot explain the word " babe " in Hebrews by the same word in the the epistles of John. In John a " babe " is one who is really on Christian ground; but here the babe is a Jewish convert who is not on Christian ground at all, who has not got beyond the " first principles " of the next chapter. As a rule, every word in Scripture is best interpreted by the book in which it is expressed. Every book in the Bible contains sufficient to explain itself; I am not to go to John or Colossians to interpret Heb. 1 have no doubt the translators of Scripture in the present day will make many mistakes as to this.
The apostle gives us in verse 14 some that are grown up. The " babe " who has got on to Christian ground is " perfect " in Hebrews. It is not a question of progress here, as it is in John.