By the word God, I assume that you mean God the Father and are asking why the Father sent the Son instead of sending himself.
It is always treacherous to presume to know God’s reasons for doing anything, but some speculation might be possible. For example, while one can choose to do something, one cannot “send” oneself. Perhaps it was important to the Father to “send” his Son. As another example, it is more sacrificial for the Father to send his Son than for him to take care of the job himself. As an analogy, consider for a moment the parent/child relationship. Parents naturally want to spare their children suffering and often feel that they would rather die themselves than see their children die. By sacrificing his own Son for the sake of humanity, the Father is taking the more difficult route than he would have had he chosen to incarnate himself.
There may, of course, be reasons that we cannot fathom this side of eternity – not to mention reasons that, in our finite limitations, we may never be able to fathom. In the end, all we can know for certain is that the Father chose the plan of salvation that he, in his omniscience, considered best.
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