Galatians 3:20

"Now a mediator cannot be of one (but must be of two parties whom he mediates between); but God is one" (not two: owing to His essential unity not admitting of an intervening party between Him and those to be blessed; but as the ONE Sovereign, His own representative, giving the blessing directly by promise to Abraham, and, in its fulfilment, to Christ, "the Seed," without new condition, and without a mediator such as the law had). The conclusion understood is, Therefore a mediator cannot appertain to God; and consequently, the law, with its inseparable appendage of a mediator, cannot be the normal way of dealing of God, the one, and unchangeable God, who dealt with Abraham by direct promise, as a sovereign, not as one forming a compact with another party, with conditions and a mediator attached thereto. God would bring man into immediate communion with Him, and not have man separated from Him by a mediator that keeps back from access, as Moses and the legal priesthood did (Exo 19:12-13, Exo 19:17, Exo 19:21-24; Heb 12:19-24).

— Jamieson-Fausset-Brown Commentary (public domain)