Hebrews 7:8

And here men that die receive tithes; but there he receiveth them, of whom it is witnessed that he liveth.

On earth the ones who collect the tithe are mortal men who die. Elsewhere the one who receives it is attested in Scripture as one who lives on, and that receiver is Melchizedek. The contrast belongs to the proof drawn from Abraham's payment of tithe to Melchizedek. That example establishes paying tithes as a duty under the Melchizedek priesthood for all who live under that priesthood.