To declare the name of the LORD in Zion, and his praise in Jerusalem;

Wesley's Notes

102:21 To declare - That they might publish the name and praises of God in his church.

Jamieson-Fausset-Brown Bible Commentary

21. To declare, &c.-or, that God's name may be celebrated in the assemblies of His Church, gathered from all nations (Zec 8:20-23), and devoted to His service.

Matthew Henry's Concise Commentary

102:12-22 We are dying creatures, but God is an everlasting God, the protector of his church; we may be confident that it will not be neglected. When we consider our own vileness, our darkness and deadness, and the manifold defects in our prayers, we have cause to fear that they will not be received in heaven; but we are here assured of the contrary, for we have an Advocate with the Father, and are under grace, not under the law. Redemption is the subject of praise in the Christian church; and that great work is described by the temporal deliverance and restoration of Israel. Look down upon us, Lord Jesus; and bring us into the glorious liberty of thy children, that we may bless and praise thy name.