4 who gave Himself for our sins to rescue us from the present evil age, according to the will of our God and Father, -Galatians 1:4 BSB
Jesus came to earth to save us from Satan’s bondage to do his will, who is the god of this world (see 2 Corinthians 4:4). Through faith in Jesus and His atoning sacrifice, we are set free.
The phrase “the present evil age” refers to the time we are living in before Christ’s millennial reign. When Jesus starts to rule, Satan and his fallen angels, the demons, will be locked up in the bottomless pit for the whole period of time during Jesus’ earthly kingdom (see Revelation 20:1-3). That time will be the closest it will ever get to having heaven on earth (see Isaiah 65:17-25). His righteousness will permeate the whole world, and people will live in true peace.
Knowing that humanity was going to fall into sin, it was the Father’s will before that time would occur to have His Son, Jesus Christ, be our payment for our sins on the cross, at His first coming.