John Calvin Commentary Psalms 115:9

"O Israel, trust thou in Jehovah: He is their help and their shield." — Psalms 115:9 (ASV)

O Israel! trust thou in Jehovah. The prophet again resumes the doctrinal point that the genuine worshippers of God have no reason to fear that He will abandon or thwart them in their time of need, because He is as willing to provide for their safety as He is equipped with the power to do so.

He proceeds, first, to exhort all the Israelites generally to place their confidence in God; second, he addresses the house of Aaron in particular; and third, he designates all who fear God. There was good reason for this arrangement.

God had adopted all the people without distinction, to whom His grace was also offered, so that they were all obligated to place their hope in Him. In accordance with this, Paul says that the twelve tribes of Israel wait for the promised deliverance (Acts 26:7). Therefore, the prophet very appropriately first addresses Israel as a whole.

But since God had in a special way set apart the Levites for Himself, and more especially the priests of the house of Aaron, to take precedence and preside over ecclesiastical matters, the prophet demands more from them than from the common people. This was not because salvation was promised specially to them, but because it was fitting that those who had the exclusive privilege of entering the sanctuary should show the way to others. It is as if the prophet had said: 'You sons of Aaron, whom God has chosen to be the teachers of religion to His people, be an example of faith to others, since He has so highly honored you by permitting you to enter His sanctuary.'