Robert Murray M'Cheyne emphasizes the vital role of the high priest in bridging the gap between sinful humanity and a holy God, explaining that before sin, there was no need for a high priest. He illustrates that Christ, as the ultimate high priest, must have something to offer, which is His own sacrifice, made out of love and necessity. M'Cheyne warns that neglecting this high priest is a grave sin, as it leads to separation from salvation. He urges listeners to recognize their need for Christ and to approach Him without hesitation, as He is the only mediator between them and God. The sermon concludes with a call to action, encouraging all to come to Christ for redemption.