John Gill Commentary Genesis 14:19

"And he blessed him, and said, Blessed be Abram of God Most High, possessor of heaven and earth:" — Genesis 14:19 (ASV)

And he blessed him
Melchizedek blessed Abram, which was one part of his office as a priest, to wish and pray for a blessing on others, see (Numbers 6:23) and herein typified Christ, who really blesses or confers blessings on all his people, even spiritual blessings, such as redemption, remission of sins, and justifying righteousness, adoption, and eternal life: and said, blessed [be] Abram of the most high God ;
that is, may he be blessed by him who is the most high God, with all kind of blessings, both temporal and spiritual; or he declares him to be blessed of him, as he undoubtedly was, or foretells that he would be, as was certainly his case: and another epithet of God is added, which abundantly shows he was able to bless him, since he is the possessor of heaven and earth ;
is the Maker of both, and has a right to dispose of all things in them, both heavenly and earthly.