Albert Barnes Commentary Psalms 37:39

"But the salvation of the righteous is of Jehovah; He is their stronghold in the time of trouble." — Psalms 37:39 (ASV)

But the salvation of the righteous is of the Lord — or, salvation comes to the righteous from the Lord. While the wicked are cut off, the righteous shall be safe. There are evidently two ideas here:

1. that there will be salvation to the righteous, while the wicked are cut off;
2. that this comes from the Lord, and not from themselves.

It is not owing to any power of their own that they are safe, but is solely because they are kept by the Lord.

He is their strength in the time of trouble — see Psalm 9:9 (note); Psalms 18:2 (note).