Jamieson, Fausset and Brown on Hebrews 3:5

5. faithful in all his house--that is in all God's house (He 3:4).

servant--not here the Greek for "slave," but "a ministering attendant"; marking the high office of Moses towards God, though inferior to Christ, a kind of steward.

for a testimony of, &c.--in order that he might in his typical institutions give "testimony" to Israel "of the things" of the Gospel "which were to be spoken afterwards" by Christ (He 8:5; 9:8, 23; 10:1).