John Gill 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
Both their temporal, spiritual, and eternal salvation; particularly the latter, which is originally of the Lord, and springs from the thoughts, purposes, and resolutions of his heart: it is of him freely, of his rich grace and abundant mercy; and it is of him fully and completely; it is an entire salvation of soul and body; includes all blessings of grace and glory in it; it is to the uttermost, and from all sin, and every enemy; and it is of him only; there is no salvation in any other; and the glory of it is to be ascribed to him, even to Jehovah, Father, Son, and Spirit; (See Gill on Psalms 3:8);

For all the three divine Persons have a concern in it: the determination, contrivance, and settlement of it, is of Jehovah the Father; the impetration or effecting of it is of Jehovah the Son; and the application of it is of Jehovah the Spirit.

[he is] their strength in the time of trouble ;
by reason of the hidings of God's face, the temptations of Satan, the prevalence of corruptions, the weakness of grace, and the many afflictions that befall them from God and men.

The Lord he is their strong hold and munition of rocks, where they betake themselves, and find help, protection, and safety; he puts underneath everlasting arms, bears them up, and upholds them with the right hand of his righteousness; and is the strength of their hearts, of their lives, and of their salvation.