Compare Douay-Rheims with King James Version side-by-side to understand the meaning.
The hundred and third psalm is a masterpiece of personal and corporate praise, beginning and ending with a summons to "Bless the Lord." The setting is the vast landscape of divine benevolence—the Lord who forgives all iniquity, heals all diseases, and redeems the life of the soul from the pit. It is a world where the crowning favor and compassion of God are as high as the heavens are above the earth. The psalmist reflects on the character of the Lord as revealed to Moses: He is merciful and gracious, slow to anger and abounding in steadfast love.
The narrative movement reveals the depth of the divine "forgetfulness" of sin. God is described as the one who does not deal with us according to our sins, but removes our transgressions "as far as the east is from the west." The central imagery is that of a father's compassion for his children; the Lord knows our frame and remembers that we are but dust. While human life is like the flower of the field that is blown away by the wind, the steadfast love of the Lord is from everlasting to everlasting. The psalm expands its scope to include the heavenly host—the angels, the ministers, and all of creation—in a universal chorus of blessing.
The theological claim of this psalm is that the "goodness" of God is the only rational explanation for the survival of the creature. It teaches that the "mercies" of the Lord are tailored to the frailty of our physical existence (our dust). The "covenant" is the framework through which this steadfast love flows to those who keep His precepts and remember His commandments. To "bless" the Lord is to proactively align one's entire being (the "all that is within me") with the beauty of His Name. True gratitude is the realization that we are treated not as we deserve, but as the King loves. Our peace is His Pardon.
The compassion of the Father was fully and finally revealed in the person of Jesus Christ, who is the "Healing" and "Forgiveness" of God made flesh. While we were still in the pit of our iniquities, Christ became the "dust" of humanity and died so that our transgressions could be removed forever. This psalm reminds us that because of Jesus, the Father's "slow anger" has been satisfied, and His abounding love is now our permanent inheritance. We are invited to join the angels in the "Blessing," knowing that our frame is held in the hand of the Son who has redeemed us. Our song is His Steadfast Love.