“Now a mediator does not mediate for one only, but God is one.”
Paul now closely relates verse 20 to the end of verse 19.
Now a mediator does not mediate for one only,
A “mediator” stands in the middle to intervene between two parties. A “mediator” stands between them and attempts to find a solution. The mediator does not represent one party but both parties. A mediator necessitates a contract between two parties, as in the Mosaic law. The law needs a mediator because it involves two parties representing both God and mankind.
but God is one
In the Abrahamic covenant, only one party signed the contract. God unilaterally signed it in grace. Grace does not operate as a mediator between two parties. Grace acts alone because it is unconditional and unilateral. There are no strings attached to God’s provision of grace.
God gives His grace unilaterally and unconditionally without strings attached.
God’s grace to us is unconditional. He puts no strings on His offer of salvation or sanctification. He Himself performs all the requirements to fulfill His side of the bargain. Salvation is all of God.
“Now all things are of God, who has reconciled us to Himself through Jesus Christ, and has given us the ministry of reconciliation, that is, that God was in Christ reconciling the world to Himself, not imputing their trespasses to them, and has committed to us the word of reconciliation” (2 Corinthians 5:18-19).