The loins, as in Ezekiel 29:7, signify the marriage of truth and good. In general, loins signify love, and when referring to the Lord, divine love. They can also signify the interiors of conjugial love. In Isaiah 11:5, they signify people in the divine good of love, and reins signify people in love towards their neighbor.

(Reference: Apocalypse Revealed 830)