Charles Ellicott Commentary Psalms 22:31

"They shall come and shall declare his righteousness Unto a people that shall be born, that he hath done it." — Psalms 22:31 (ASV)

They shall come — that is, the generation just foretold: it will announce His righteousness to a still younger generation (literally, to a people born), that He accomplished. The tale of Jehovah’s goodness to Israel would be handed on from age to age,

“His triumphs would be sung
By some yet unmoulded tongue.”