Albert Barnes Commentary Psalms 74:2

"Remember thy congregation, which thou hast gotten of old, Which thou hast redeemed to be the tribe of thine inheritance; [And] mount Zion, wherein thou hast dwelt." — Psalms 74:2 (ASV)

Remember your congregation - The word rendered “congregation” properly means an “assembly,” a “community,” and it is frequently applied to the Israelites, or the Jewish people, considered as a body or a community associated for the service of God (Exodus 12:3; Exodus 16:1–2, 9; Leviticus 4:15; Numbers 27:17). The word used by the Septuagint is συναγωγή sunagōgē – synagogue – but refers here to the whole Jewish people, not to a particular synagogue or congregation.

Which you have purchased of old - In ancient times; in a former age. That is, you have “purchased” them for yourself, or as your own, by redeeming them from bondage, thus securing to yourself the right to them, as one does who redeems or purchases a thing. See the notes at Isaiah 43:3.

The rod of your inheritance - Margin, as in Hebrew, “tribe.” The Hebrew word – שׁבט shêbet – properly means “a staff,” stick, rod; then, a shepherd’s staff, a crook; then, a scepter; and then it is used to denote a “tribe,” so called from the staff or scepter which the chief of the tribe carried as the symbol of authority (Exodus 28:21; Judges 20:2).

The word “inheritance” is frequently applied to the children of Israel considered as belonging to God, as property inherited belongs to the one who owns it – perhaps suggesting the idea that the right to them had come down, as inherited property does, from age to age. It was a right over them acquired long before, in the days of the patriarchs.

Which you have redeemed - By delivering them out of Egyptian bondage. So the church is now redeemed, and, as such, it belongs to God.

This mount Zion - Jerusalem – the seat of government and of public worship – the capital of the nation.

Where you have dwelt - By the visible symbol of your presence and power. On all these considerations, the psalmist prays that God would not forget Jerusalem in the present time of desolation and trouble.