Yes, Satan exists, and the Old Testament reveals him as the enemy of God and humanity (Genesis 3:15). Originally created as an angel named Lucifer, he rebelled against God out of pride and was cast out of heaven (Isaiah 14:12–17; Ezekiel 28:11–17). In the Garden of Eden, Satan deceived Adam and Eve, leading them into sin, and he continues to use lies to oppose God’s truth (Genesis 3:1–6). Throughout Scripture, Satan is described as the accuser and adversary, working to turn people away from God (Revelation 12:10; Job 1:6–12). Though his opposition persists, Jesus's victory on the cross guarantees Satan's eventual defeat in the final judgment (Revelation 19:20; 20:7–10).
We can submit our own individual lives to Jesus and place them under His authority. When we are living for Jesus Christ, we can trust that God living in us is greater than Satan, and we need not fear him or succumb to his attacks against us (Luke 10:17–20; 1 John 4:4). As we submit to God, we can resist the devil, and he has to flee (James 4:7).
By reading the Bible, we learn how Satan operates. The power of God will always be greater than the power of Satan, but we have to remain aware that we are in a spiritual battle that will not end until Jesus returns (Ephesians 6:10–18). We can be confident in the fact that Jesus defeated Satan once and for all at the cross, and when the final judgment occurs, Satan's eternal end is guaranteed (Revelation 19:20; 20:7–10).