Charles H. Spurgeon on Psalms 135:19

Bless the LORD. Blessing of God is to wish well to, and speak well of God, out of goodwill to God himself, and a sense of his goodness to ourselves. God loves your good word, that is, to be spoken of well by you; he rejoiceth in your well wishes, and to hear from you expressions of rejoicings in his own independent blessedness. Though God hath an infinite ocean of all blessedness, to which we can add nothing, and he is therefore called by way of eminency, "The Blessed One" (Mr 14:61), a title solely proper and peculiar to him, yet he delights to hear the amen of the saints, his creatures, resounding thereto; he delights to hear us utter our "so be it." —Thomas Goodwin.