Because [his/her/its] sense of humor is ineffable.
Seriously?? I've asked this question about 100,000,000 times. Answers: "Before I formed you in your mother's womb..." "I know the plans I have for you..." "Where was thou when I made the wild goats..."
Blah, blah, blah. Basically, "I have my reasons." "That's for Me to know and you to figure out." Some variation on, "I have set you apart for reasons I don't care to explain." "Because I said so."
The closest things I have ever gotten to real answers involve the idea of being set apart, to be "in the world but not of it." The best answer I have ever gotten is, more or less, "So you would have eyes to see and ears to hear and the inclination to look and listen."
Cold comfort, small solace.
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"Alas, our dried voices when we whisper together are quiet and meaningless, as wind in dry grass, or rats' feet over broken glass in our dry cellar." --TS Eliot, "The Hollow Men"