1. When the time of Christ is fulfilled (Mk 1:15)
    Dan 9:24-26, Gal 4:4, 1 Tim 2:6

In the Old Testament it was foretold when Christ would come. (Dan 9:24-26)

Dan 9:24 Seventy weeks are determined upon thy people and upon thy holy city, to finish the transgression, and to make an end of sins, and to make reconciliation for iniquity, and to bring in everlasting righteousness, and to seal up the vision and prophecy, and to anoint the most Holy.
25 Know therefore and understand, that from the going forth of the commandment to restore and to build Jerusalem unto the Messiah the Prince shall be seven weeks, and threescore and two weeks: the street shall be built again, and the wall, even in troublous times.
26 And after threescore and two weeks shall Messiah be cut off, but not for himself: and the people of the prince that shall come shall destroy the city and the sanctuary; and the end thereof shall be with a flood, and unto the end of the war desolations are determined.

The time of Christ is fulfilled. In other words, the time has come for Christ to come and begin the work of Christ. Jesus began the work of Christ. (Mk 1:15, Gal 4:4, 1 Tim 2:6)

Mk 1:15 And saying, The time is fulfilled, and the kingdom of God is at hand: repent ye, and believe the gospel.

Gal 4:4 But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law,

1 Tim 2:6 Who gave himself a ransom for all, to be testified in due time.