Consider how great Melchizedek was: Even the patriarch Abraham gave him a tenth of the plunder.
4. Now consider, etc. This is the fourth comparison between Christ and Melchisedec, that Abraham presented tithes to him. But though tithes were instituted for several reasons, yet the Apostle here refers only to what serves his present purpose. One reason why tithes were paid to the Levites was, because they were the children of Abraham, to whose seed the land was promised.
The foregoing chapter ended with a repetition of what had been cited once and again before out of Psa 110:4, Jesus, a high priest for ever, after the order of Melchisedec. Now this chapter is as a sermon upon that text; here the apostle sets before them some of the strong meat he had spoken of before, hoping they would by greater diligence be better prepared to digest it. I.
Commenting on Hebrews 7:1-10
Now consider how great this man was,.... Melchizedek, of whom so many great and wonderful things are said in the preceding verses: and as follows, unto whom the patriarch Abraham gave the tenth of the spoils; of Abraham's giving tithes to him; see Gill on Heb 7:2 and Melchizedek's greatness is aggravated, not only from this act of Abraham's, but from Abraham's being a "patriarch"...