Jamieson, Fausset and Brown on Hebrews 3:2

2. He first notes the feature of resemblance between Moses and Christ, in order to conciliate the Hebrew Christians whom He addressed, and who still entertained a very high opinion of Moses; he afterwards brings forward Christ's superiority to Moses.

Who was faithful--The Greek implies also that He still is faithful, namely, as our mediating High Priest, faithful to the trust God has assigned Him (He 2:17). So Moses in God's house (Nu 12:7).

appointed him--"made Him" High Priest; to be supplied from the preceding context. Greek, "made"; so in He 5:5; 1Sa 12:6, Margin; Ac 2:36; so the Greek fathers. Not as Alford, with Ambrose and the Latins, "created Him," that is, as man, in His incarnation. The likeness of Moses to Messiah was foretold by Moses himself (De 18:15). Other prophets only explained Moses, who was in this respect superior to them; but Christ was like Moses, yet superior.