John Gill Commentary Psalms 126:5

"They that sow in tears shall reap in joy." — Psalms 126:5 (ASV)

They that sow in tears shall reap in joy. A proverbial expression, encouraging faith in prayer put up for the return of the captivity, whether in a literal or spiritual sense. Praying or seeking the Lord is sowing in righteousness, (Hosea 10:12); which is often attended with tears and weeping; the issue of them is not always seen soon: these, like seed, lie buried under the clods, but take effect and will rise up in due time: saints should wait patiently for a return of them, as the husbandman for the fruits of the earth; in due time they will produce a large crop of blessings, a plentiful harvest, which the praying saint will reap with joy; as those that prayed and waited for the redemption in Jerusalem; and as those that pray for the latter day glory, the conversion of the Jews, the fulness of the Gentiles, and the destruction of antichrist; the souls under the altar have been sowing in tears, but before long they will reap in joy, (Revelation 6:9) (Revelation 19:1Revelation 19:2).

It may be applied to the state and condition of saints in common in this life; now is their sowing time, and careful they should be that they sow not to the flesh, but to the spirit: and a sorrowful time it is, on account of inward corruptions, Satan's temptations, divine desertions, and the imperfection of their services; but before long they will reap life everlasting, reap in joy, and be in the fulness of it; now they weep, then they shall rejoice; now they mourn, then they shall be comforted.