Will Jesus return and if so, why? He is said to have saved already all people on the cross.

Answer:

The Old Testament already speaks of the Day of the Lord on which God would punish all evil deeds of his peoples but also save his peoples and restore it. What is meant here becomes truly apparent only in the New Testament: We expect the day of Jesus Christ, his coming again in glory. Then Jesus will be revealed to all humanity. He is the Judge of the living and the dead, a right granted to him by God. The Bible prophesies this event with majestic imagery. All the relevant passages of the New Testament say the one thing: At the end, Christ will triumph and with him truth and justice. The lowly and the humiliated, the forgotten, the victims of terror and disasters will come into their own, all evil and unjust violence will cease to be. Thus the message of the Judgement of the world is a wholly joyful message. [...]

And so we [Christians] expect that Jesus will complete history. This is a joyful message and at the same time something that has enormous relevance today. Not we achieve the completion of the world but the Lord. Whoever has understood this will no longer follow a prophet of earthly paradise. We Christians will not be confused by the ups and downs of world history. We must fight valiantly for justice in the world, do as much good as we can, but we should not expect completion from ourselves. And so the hope for the Victor and Judge Jesus Christ protects us from bad utopias which, as history clearly shows, often end in blood and tears. False hope of an earthly paradise, slow resignation without hope: the message of Christ’s coming again in glory protects us from both.

(Wilfried Henze, „Glauben ist schön. Ein Katholischer Familienkatechismus.“ Harsum: Harsum, 2001, p. 176-177).