Albert Barnes Commentary Psalms 122:4

"Whither the tribes go up, even the tribes of Jehovah, [For] an ordinance for Israel, To give thanks unto the name of Jehovah." — Psalms 122:4 (ASV)

Where the tribes - The twelve tribes of the children of Israel.

Go up - To the great feasts and festivals of the nation. See Exodus 23:17. This language of “going up” is similar to what would be used anywhere regarding the capital of a nation—as it is now of London—but it was literally true of Jerusalem, since it was elevated far above most parts of the land.

The tribes of the Lord, to the testimony of Israel - The “ark of testimony;” the ark in which were the tables of stone, containing the law considered as God’s testimony or witnessing to justice, right, equity, duty, truth. See Exodus 16:34; Exodus 25:16, 21; Exodus 40:3, 20; Exodus 30:6, 36; Exodus 31:18.

To give thanks to the name of the Lord - To worship Yahweh—the name often representing the Being himself. A main part of Hebrew worship was praise, and therefore, this often represents the whole of worship.