loose
Not firmly or tightly fixed in place; detached or able to be detached.
2. free from anything that binds or restrains; unfettered:
20. to let loose; free from bonds or restraint.
21. to release, as from constraint, obligation, or penalty.
22. Chiefly Nautical. to set free from fastening or attachment: to loose a boat from its moorings.
23. to unfasten, undo, or untie, as a bond, fetter, or knot.
24. to shoot; discharge; let fly: to loose missiles at the invaders.
25. to make less tight; slacken or relax.
26. to render less firmly fixed; lessen an attachment; loosen.
That’s the adjective. He’s using loose as a verb, to set free. That which shall be loosed in heaven shall be loosed on earth. Archaic, but still proper.