The Living Water by William Arkle
This is a fundamental question - and perhaps one that it is hazardous to avoid answering.
Of course one can say, many have said, that this is a permanent and necessary mystery, or that God's creation was a gratuitous (hence meaning-less) act. Christians often say that God created from an abundance of love, but keeping this very abstract - in an attempt to make clear that God's love is neither necessary nor gratifying to God...
Some reasons why A God might create are bad ones, from our point of view - there might be an evil God who created a world of beings in order that he could enjoy their suffering, could torment them - and certainly some people do seem to believe exactly this (e.g. they believe this is the truth about the God that Christians worship).
Or God might be indifferent to his creature, it not mattering one way or the other whether individual or en masse the Beings are happy or suffering.
Furthermore, there are ideas about what role the Beings, such as ourselves, have; and perhaps most types of theism have no necessary role for Men: by this account, Men cannot help or harm creation, because creation is entirely God's business.
But the religion brought by Jesus is a very personal religion, and tells us that God is a person, Jesus is a person, Men are persons - and God, Jesus and Men are linked by loving family relationships - they/ we are part of the same family.
This makes Christian creation a very much more personal thing than in some abstract schemata of creation. God does not so much 'make' Men as procreate children; and implicitly for the same kind of reason/s that Men procreate children, at the highest level of human love.
Creation and procreation become, for Christians, part of the same qualitative activity. The making of Beings (which compose every-'thing' that is created) and of Human Beings is part of the same activity.
And we know, from introspection - and from what we know of God (because as children we have God within us), that creation comes from love; and creation is 'rewarding' to the creator, as well as being a gift to the created.
Christians should not shy-away from the fact that God created because it gratified him to do so - in simple language, God is happier in the midst of Creation than in isolation - as most men (and all Good Men, all who choose salvation) are happier with a family, than without.