John Calvin Commentary Psalms 122:9

"For the sake of the house of Jehovah our God I will seek thy good." — Psalms 122:9 (ASV)

Because of the house of Jehovah our God, etc. In this verse, he adds a second reason why he cared for the Church—that he did so because the worship of God, far from remaining intact, would go to ruin unless Jerusalem continued to stand. If, then, the salvation of our brethren is important to us, if religion is for us a heartfelt commitment, we ought, at the same time, as much as we are able, to take an interest in the prosperity of the Church.

From this it follows that those who are indifferent about her condition are no less cruel than impious; for if she is the pillar and foundation of truth, the inevitable consequence of her destruction must be the extinction of true piety. And if the body is destroyed, how can each of the members fail to be involved in destruction?

Furthermore, this passage teaches us that the Church is not an empty title, but must be sought where true religion prevails. Thus it appears how foolish the Papists are, who, despite having rejected and overthrown the doctrine of the Gospel, yet mightily boast of the name of the Church.