Albert Barnes Commentary Psalms 35:9

"And my soul shall be joyful in Jehovah: It shall rejoice in his salvation." — Psalms 35:9 (ASV)

And my soul shall be joyful in the Lord - That is, I will be joyful, or will rejoice. This is said in anticipation of God's intervention in destroying his enemies and in delivering him from danger.

It is not joy in the destruction of others; it is joy that he himself would be delivered. Our own deliverance from the hand of our enemies may involve the necessity of their being cut off. What we rejoice in, in such a case, is not their ruin, but our own deliverance; and for this it can never be improper to give thanks.

The psalmist says that he would rejoice “in the Lord.” It would not be in his own skill or courage, but in what God had done to save him. See the notes at Psalm 34:2.

It shall rejoice in his salvation - For the salvation or deliverance that he brings to me.