Matthew Poole and continuators on Genesis 14:19

19 And he blessed him, and said, Blessed be Abram of the Most High God, possessour of Heaven and Earth.

Or, Therefore (as the particle is oft taken, (i. e.) because he was a Priest of God) he (i. e.) Melchizedek) blessed him, (Abraham) which was one act of the Priestly Office. See on Heb. 7. 6, 7.

So it is a prayer for him that God would confirm and increase the blessing which he had given him. Or, Blessea is: So it is an acknowledgement of Gods blessing conferred upon Abraham both formerly and in this late and great victory. Or, blessed shall be: So it is a prediction concerning his future and further blessedness, whereof this was only an earnest.