Samuel Rutherford (Communion Sermons, 118-119):
The Lord's calling Christ is His giving Him law on His side, by a public office; to teach as a Prophet, to suffer as a Priest, and to subdue, rule, and defend, as a King. For we may know for certain, that howbeit Christ-man had a private goodwill to us, pitying our case, and desiring we should be set at liberty; yet that would not have done our turn, except He had been a divine person, and given the required satisfaction. A man may have a good-will to be cautioner [guarantor] and surety for another; but if he is a rebel against the king, the law cannot accept of him. No, he cannot be accepted unless he be a free subject, and a sponsible man [a man able to pay]. So Christ having man's bowels to pity us, God gave Him law upon His side, and public authority against all sin. Here is a singular comfort to all weak, sick, and heavy-laden souls. If ye doubt of your salvation, remember that Christ by law, and God's good-will and special calling, is made and appointed a Mediator for you. Then it is no false pretension that Christ took your plea in hand: He has a calling to it by law. Then rest and rely upon Him alone for salvation. The Lord has made a resignation of you over to Christ; and if ye truly believe in Him as He is offered to you in the everlasting gospel, there is no fear that He cast you off or that ye shall not be saved. Whom He loves, He loves unto the end. If ye are His, He will not lose His right. Then boldly claim salvation, forgiveness, and Christ's righteousness. It is yours by God's calling; take your own, and be not driven from it as silly bodies: be not bosted [driven by threats] from salvation, by temptations, crosses, and faithless fears. If you believe in Christ, your rights are strong. Christ says, “The Lord God called Me from My mother's womb:" that may be your warrant, to trust in Him as an all-sufficient Saviour.