Charles H. Spurgeon on Psalms 115:10

O house of Aaron, trust in the LORD. You who are nearest to him, trust him most; your very calling is connected with his truth and is meant to declare his glory, therefore never entertain a doubt concerning him, but lead the way in holy confidence. The priests were the leaders, teachers, and exemplars of the people, and therefore above all others they should place an unreserved reliance upon Israel's God. The Psalmist is glad to add that they did so, for he says, He is their help and their shield. It is good to exhort those to faith who have faith: "These things have I written unto you that believe on the name of the Son of God; ...that ye may believe on the name of the Son of God." We may stir up pure minds by way of remembrance, and exhort men to trust in the Lord because we know that they are trusting already.