The return of Christ has two phases.
In Matt 24:3-14 Jesus gave the sign of his "parousia" (presence) and the "end of the age".....or the end of the present system of things, and the way it operates today. The world and its whole way of governance and worship will change, suddenly and dramatically. Man's corrupt mismanagement of this planet will be stripped away from him. (Dan2:44)
Since Jesus gave a "sign", not of his 'coming', but of his 'presence', it is apparent that this first phase is not a visible event. Why would a sign be necessary for something everyone can see?
Christ's presence is connected to a series of events that would indicate that he was ruling in his kingdom and that the last days of this system of things had begun. During this period, we would witness global war, food shortages, diseases, great earthquakes and an increase in lawlessness. The love of neighbor seen in times past would grow cold and the world would become burdened down by those who profess godly devotion but whose conduct is anything but. People's personalities would change for the worse. (2 Tim 3:1-5)
This was also the time for a global preaching of the good news of God's kingdom....the only true hope for peace and security on the earth. Those who responded to the kingdom message would become part of God's "people" by removing themselves from "Babylon the great" (any and all modes of false worship) and coming to God's mountain...the seat of his holy worship. (Isa 2:2-4) They will learn to be peace loving disciples of God's son who will not become embroiled in the world's conflicts or political struggles. For this, the world would hate them. (John 15:18-21)
Only when all those things had taken place, would "the end" come.
Jesus is then seen to arrive with his angelic forces to judge the world. Phase one is complete and now phase two begins.
As God's appointed judge, Jesus will 'gather the nations together and separate the people one from another, just like a shepherd separates sheep from goats.'
One group (sheep) will be granted life, whilst the others (goats) will be sentenced to everlasting death.
All will have been given ample opportunity to hear and respond to the message delivered by God's people all over the world.
God wants all to come to him in repentance, but he knows that relatively "few" will do so.
(Matt 7:13, 14, 21-23; 2 Pet 3:8-13)