How do we know that Christ's victory over Satan is assured?

The assurance of Christ's victory over Satan is rooted in both His incarnation and redemptive work. Revelation 12 describes the birth of Christ, who came to save His people, and highlights that while Satan attempted to thwart God's plan by trying to destroy the child, he ultimately failed (Revelation 12:4-5). Furthermore, Christ's death and resurrection delivered the ultimate blow to Satan, crushing his power and securing redemption for His people. As noted in Revelation 12:10-11, the accuser of the brethren has been thrown down, and through Christ's blood, His people are victorious over sin and accusation. This demonstrates that no matter the attempts of Satan, his defeat is guaranteed by the sacrifice of Christ.