The simple answer to this question is ‘for His glory’. That is why God does anything, or everything, it is to glorify Himself.
For reasons we cannot know, God did not think that creating us and having us fixed in His presence from the beginning would be the way He would be most glorified. The entire history of creation and humanity is the story of God revealing His glory, and so nothing is by accident. God intended to glorify Himself through all that has and will happen.
We read in Revelation 4:11, “Thou art worthy, O Lord, to receive glory and honour and power: for thou hast created all things, and for thy pleasure they are and were created.” And that’s it in a nutshell, everything was created and ordered in the way that would bring pleasure to God and glory to His name.
The question we must ask ourselves is, am I living my life for the purpose of glorifying God? That is the purpose of your existence.
Armen