Biblical Eschatology is a study of things to come. The Second Advent of Jesus is one of the eschatological issues in Christian theology. Mainstream Christians believe that Jesus, forty days after his resurrection ascended to heaven and he will return to Earth at the end of time. One of the main Biblical references for the second advent of Jesus is in the Acts of the Apostles.
“Upon saying this and while they were looking on, he was taken up and a cloud carried him up from their view. And as they kept gazing intently toward heaven as he was going away from them, two men in white clothing were standing by them, who also said: Men of Galilee, why do you stand gazing into heaven? This very Jesus, who was taken up from you into heaven, will come again in the same way you have seen him going to heaven.” (Acts 1:9-11)