From the additional notes by other writers in Charles Spurgeon's The Treasury of David: Psalm 103.
Verse 1. Bless the LORD, O my soul.
You have often heard, that when God is said to bless men, and they on the other hand are excited to bless him, the word is taken in two very different senses. God is the only fountain of being and happiness, from which all good ever flows; and hence he is said to bless his creatures when he bestows mercies and favours upon them, gives them any endowments of body and mind, delivers them from evils, and is the source of their present comforts and future hopes. But in this sense, you will see there is no possibility of any creature's blessing God; for as his infinite and unblemished perfection renders him incapable of receiving any higher excellency, or improvement in happiness; so, could we put the supposition that this immense ocean of good might be increased, it is plain that we, who receive our very being and everything that we have or are from him, could in no case contribute thereto.
To bless God, then, is, with an ardent affection humbly to acknowledge those divine excellencies, which render him the best and greatest of beings, the only object worthy of the highest adoration: it is to give him the praise of all those glorious attributes which adorn his nature, and are so conspicuously manifested in his works and ways. To bless God, is to embrace every proper opportunity of owning our veneration and esteem of his excellent greatness, and to declare to all about us, as loudly as we can, the goodness and grace of his conduct towards men, and our infinite obligations for all our enjoyments to him, in whom we live, move, and have our being. And a right blessing of God must take its rise from a heart that is full of esteem and gratitude, which puts life into the songs of praise. And then, of all others, the most lively and acceptable method of blessing God, is a holy conversation and earnest endeavor to be purified from all iniquity; for blessing of God consists, as I told you, in adoring his excellencies, and expressing our esteem and veneration of them: but what can be so effectual a way of doing this, as the influence that the views of them have upon our lives?
That person best exalts the glory of the divine power, who fears God above all, and trembles at the apprehensions of his wrath; and of his justice, who flees from sin, which exposes him to the inexorable severity thereof; and of his love, who is softened thereby into grateful returns of obedience; and then we celebrate his holiness, when we endeavour to imitate it in our lives, and abandon everything that is an abomination to the eyes of his purity. William Dunlop, 1692-1720.