Moses and Aaron were his priests,

    and Samuel was one who prayed to him;

    they called to the Lord, and he answered them. – Psalm 99:6 GNT

Moses, Aaron and Samuel were just the few who made it their life’s business to call on God in prayer. When they did, they brought blessings upon themselves and others. When they called on God, He answered them. Their prayers were not useless because they knew God was a holy God and therefore true to His promises. He heard them all in full view of the mercy-seat. I can imagine if our God was unholy then it would be natural for Him to be false to His word and even refuse to hear His people’s cry, regardless of who they were. However, this verse establishes a truth meant for our joy and God’s glory, that men of God who follow Him never offered useless prayers.

“Prayer is practically universal in the human race. . . . All the non-Christian religious systems involve the practice of some kind of prayer. Non-Christian prayer, however, is not addressed to the . . . Triune God of the Scriptures . . . That God in his great mercy may sometimes hear and answer the prayers of non-Christians . . . we should not deny. But such prayers differ essentially from Christian prayer.” Johannes G. Vos