Five times in the two psalms that open Bless the Lord, O my soul (Psalms 103 and 104), David addresses his own soul. Why five? The Rabbis of the Talmud (Berakhot 10a) answer: because the soul possesses five properties that mirror five attributes of God Himself.
As God fills the whole world, the soul fills the whole body. As God sees and is not seen, the soul sees and is not seen. As God nourishes the whole world, the soul nourishes the whole body. As God is pure, the soul is pure. As God dwells in secret, the soul dwells in secret.
"Therefore," the sages conclude, "let the one who possesses these five properties praise Him to whom these five attributes belong." The soul is not a pale spark of the Divine. It is a working likeness. It does, on the scale of a single body, what God does on the scale of creation.
This teaching, preserved in the 1901 anthology Hebraic Literature, reframes what David is doing in those two psalms. He is not performing piety. He is whispering to the part of himself that already knows the One being praised. Bless the Lord, O my soul is the only honest prayer a soul can pray, because the soul alone understands, from the inside, what blessing means.