What is the Second Coming?
Isaiah's prophecy of the Messiah (Christ) tells of a suffering Servant who was "pierced for our offenses, /crushed for our sins" (ls 53:5; see ls 53:1-12). Jesus fulfilled this prophecy when he died on the cross for us (see 1 Pt 2:24-25). But there are other prophecies of Christ, still unful filled, that point to a different scenario: a glorious King, a powerful judge, who comes to rule the earth (see Rv 19:11-16).
The prophet Daniel, for example, foresaw "One like a son of man coming, / on the clouds of heaven" who receives "dominion, glory, and kingship; / nations and peoples of every language serve him. / His dominion is an everlasting dominion" (Dn 7:13-14).
At Jesus' ascension into heaven, angels confirmed what he had earlier promised: He will return one day to earth (see Acts 1:10-11). Why is it necessary for him to return? Because his mission on earth is not yet complete: He came the first time as our suffering Redeemer, but he must return as our holy judge.
Christ's life, death, resurrection, and ascension form only part of the gospel, the "good news" of our redemption. The rest of the gospel is the good news that God is not only merciful but also just. One day Christ will come back to set the world aright, and the evil one will at last be rendered utterly powerless to harm those who love God (see Rv 20:10, 14).
Even now Jesus reigns as Lord of all at the Father's right hand in heaven (see Eph 1:20). But when Christ returns, God's kingdom will finally come to us in all its fullness, and God's will at last will be done "on earth as in heaven" (Mt 6:10).
Yet another aspect of divine justice will be fulfilled when Christ returns: He will be vindicated and honored in the eyes of all the world. Even those who have "spurned and avoided [him]" (ls 53:3) will be compelled to bend their knees before him at last and "confess that /Jesus Christ is Lord, / to the glory of God the Father" (Phil 2:10-11).