Robert Anderson emphasizes the supremacy of grace in the Gospel, illustrating how God's glory is revealed through His sovereign grace. He warns against preaching a mixed gospel that undermines God's glory and the hope of sinners, stressing that salvation is solely through the blood of Christ and the grace it brings. Anderson explains that the death of Christ marked a pivotal moment in history, where grace triumphed over sin, allowing for the possibility of eternal life for all who believe. He highlights that grace reigns not at the expense of righteousness but through it, affirming that God's blessings are available to all, regardless of their past. Ultimately, he calls believers to rejoice in the grace that has been extended to them through Christ's sacrifice.