But I [am] like a green olive tree in the house of God,.... Or rather it should be supplied, "I shall be" ; since David was at this time an exile from the house of God: and this expresses his faith and confidence, that, notwithstanding his present troubles, he should be restored again, and be in a very flourishing condition, in the church of God; which is here meant by "the house of God": it being of his building, and where he dwells, and where to have a place is the great privilege of the saints; they are planted there by the Lord himself, and shall never be rooted up; they are fixed there, and shall never go out; which was David's confidence, Ps 23:6; and where he believed he should be as "a green olive tree"; which is a very choice and fruitful tree, has fatness in it, produces an excellent oil; is beautiful to look at; delights in hot climates and sunny places; is found on mountains, we read of the mount of Olives; is ever green and durable, and its leaves and branches are symbols of peace: all which is applicable to truly righteous persons and believers in Christ; who are the excellent of the earth, are filled with the fruits of righteousness; are fat and flourishing; have the oil of grace, the anointing which teacheth all things; are a perfection of beauty, made perfectly comely through Christ's comeliness; thrive under him, the sun of righteousness; grow in the mountain of the Lord's house, the church: their grace is incorruptible, their leaf withers not; they are rooted in Christ, and ever continue; they are the sons of peace, and their last end will be eternal peace.
Now as such David was assured he should be, when his enemy would be rooted up out of the land of the living, and cast like a dry and worthless branch into everlasting burnings; the ground of which confidence follows:I trust in the mercy of God for ever and ever; the mercy of God is not only an encouragement to trust, but the object of it; not the absolute mercy of God, but the grace and goodness of God in Christ Jesus, which endures continually, Ps 52:1; and so does hope in it, which never makes ashamed, but abides to the end.
The psalmist seems to have respect to the mercy promised him, that he should sit upon the throne. This he believed, and therefore was assured he should be in the flourishing circumstances in the house of God before mentioned.