Albert Barnes Commentary Psalms 102:13

"Thou wilt arise, and have mercy upon Zion; For it is time to have pity upon her, Yea, the set time is come." — Psalms 102:13 (ASV)

Thou shalt arise - You will come forth - as if God had been inattentive or inactive.

And have mercy upon Zion - That is, upon Jerusalem, represented as in a state of desolation. God would eventually pity her and intervene on her behalf.

For the time to favor her - Implying that there was an appointed time to favor her, or to bring her troubles to an end.

Yea, the set time is come - The word used here - מועד mô‛êd - properly means an appointed season, a designated moment. It refers to some purpose or appointment regarding anything that is to be done, as in (1 Samuel 13:8, 11); (2 Samuel 20:5); (Genesis 17:21); or to a fixed period, as when certain things are to be done, or certain festivals are to be held regularly at a particular season of the year, (Lamentations 1:4); (Lamentations 2:6); (Hosea 9:5); (Hosea 12:9); (Leviticus 23:2, 4, 37, 44).

In this context, it means that there was some period fixed in the Divine Mind when this was to occur, or a definite time when it had been predicted or promised that it would occur. The language is that which would be applicable to the captivity in Babylon, concerning which there was a promise that it would continue only seventy years.

If the psalm refers to that, then the meaning is that there were indications in the course of events that this period was about to arrive. Compare the notes at (Daniel 9:2). The psalmist immediately states what those indications were in this case (Psalms 102:14).

It may be noted here that there are usually some previous intimations or indications of what God is about to do. “Coming events cast their shadows before.” Even divine purposes are usually accomplished in connection with human agency and in the regular course of events, and it is frequently possible to anticipate that God is about to appear for the fulfillment of His promises.

So it was in the coming of the Savior. So it was in the destruction of Jerusalem by the Romans. So it is when God is about to revive religion in a church. So it is, and will be, regarding the conversion of the world.