John Calvin Commentary Psalms 99:6

"Moses and Aaron among his priests, And Samuel among them that call upon his name; They called upon Jehovah, and he answered them." — Psalms 99:6 (ASV)

Moses and Aaron. The Psalmist magnifies the special grace which God, in a very remarkable manner, bestowed upon the seed of Abraham, that from them he chose for himself prophets and priests to be, as it were, mediators between him and the people, to ratify the covenant of salvation. And he mentions three persons who were famous in former times.

For Moses was, as it were, a mediator to reconcile the people to God. Aaron was invested with the same office; and, subsequently, Samuel fulfilled the same role. There is no doubt, however, that under these three persons he included all the people with whom God had made a covenant.

But he mentions the names of those who were the custodians and guardians of this invaluable treasure. It may appear improper that he should speak of Moses as among the priests, since his sons were only among the common Levites, and that Moses himself, after the giving of the law, never held the office of high priest.

But as the Hebrews call כוהנים, chohanim, those who are chief and very eminent individuals, such as kings’ sons, nothing prevents the prophet from giving this designation to Moses, as if he had said that he was one of the holy rulers of the Church. Moreover, if we go back to the earliest period—to the time before the publication of the law—it is certain that Moses was then invested with the high priest’s office.

The prophet’s purpose must also be kept in mind: namely, that God not only adopted the seed of Abraham but also set apart some of them to act as mediators, whom he instructed to call upon his name, so that his covenant might be further confirmed. For the invocation of which he speaks must not be understood indiscriminately to mean every kind of calling upon, but only that which belongs to the priests, who were chosen by God as intercessors to appear in his presence on behalf of all the people and to speak for them.

They called upon Jehovah. The Psalmist explains more fully what I have just said: that God from the very beginning, and specifically in relation to his gracious covenant, bestowed great benefits upon the descendants of Abraham—the Jews. And, therefore, whenever they experienced the loving-kindness of God, they needed to remember his previous loving-kindness.

The prophet also makes particular mention of the visible symbol of the cloudy pillar, by which God intended to testify in all ages that his presence was always with his people. He employed temporal signs not only for the benefit of those to whom they were shown but also for the benefit of those who would succeed them.

This is not to say that God always showed a cloudy pillar to his ancient people. However, considering that human dullness is so great that people do not perceive God's presence unless reminded by external signs, the prophet rightly reminds the Jews of this memorable sign.

And just as God had appeared openly in the desert to their ancestors, so their descendants could be well assured that he would also be near them. The prophet adds that they had kept God’s testimonies, in order to impress the duty of similar obedience upon succeeding generations.