Isaiah 65:18

18.But rejoice ye and be glad for ever. He exhorts believers to rejoice, in such a manner as they ought, on account of such a benefit bestowed by God. And this was added for the sake of amplification; because men do not adequately consider God’s other benefits, and especially that which is the highest and most excellent of all; for either they disregard them altogether, or value them less than they ought to do. On this account believers must be aroused and urged by such exhortations as these, that they may not chew themselves to be unthankful or unmindful, or think that it ought to be lightly passed by, that, having been redeemed by the hand of Christ, they carry in their hearts the pledge of eternal and heavenly life. That is the reason why Isaiah chews that believers do not give due praise for redemption in any other way than by continuing their joy through the whole course of their life, and employing themselves in celebrating the praises of God.

For, lo, I create Jerusalem a rejoicing, and her people a joy. At first sight this might be thought harsh; but an excellent meaning is obtained, that the ground of joy in the deliverance of the Church shall be so great as to remove every cloud of sadness. And, indeed, since even afflictions aid our salvation, (Romans 8:28,) we have good reason for rejoicing in them.