John Calvin Commentary Hebrews 3:2

"who was faithful to him that appointed him, as also was Moses in all his house." — Hebrews 3:2 (ASV)

Who was, or is faithful, etc. This is a commendation of the apostleship of Christ, so that the faithful may securely trust in him. He commends it on two grounds: because the Father has set him to be over us as our teacher, and because Christ himself has faithfully performed the office committed to him.

These two things are always necessary to secure authority for a doctrine. For God alone ought to be heeded, as the whole Scripture testifies. Therefore, Christ declares that the doctrine which he delivered was not his own, but the Father’s (John 7:16); and in another place he says, “He who received me, receiveth him who has sent me.” (Luke 9:48). For we say of Christ that, as he is clothed with our flesh, he is the Father’s minister to carry out his commands.

To the calling of God is added Christ's faithful and upright performance of duty; and this is required of true ministers, so that they may obtain credence in the Church. Since these two things are found in Christ, undoubtedly he cannot be disregarded without despising God in him.

As also Moses, etc. Omitting the priesthood for a while, he speaks here of Christ's apostleship.

For as there are two parts in God’s covenant—the promulgation of the truth and, so to speak, its real confirmation—the full perfection of the covenant would not appear in Christ if both parts were not found in him. Therefore, the writer of the epistle, after mentioning both, roused attention with a brief exhortation. But he now enters into a longer discussion and begins with the office of a teacher; therefore, he now compares Christ only with Moses.

The words in all his house, may be applied to Moses, but I prefer to apply them to Christ, as Christ may be said to be faithful to his Father in ruling his whole house. It therefore follows that none belong to the Church of God except those who acknowledge Christ.