According to midrashic legend, every soul created by God has all knowledge of the universe. . . .
So, according to legend, just before a soul, now placed into the body of a baby in the womb, emerges into human life, an angel, whose name is Lailah, taps the baby on the upper lip — creating the little indentation we call the philtrum — and in doing so takes away the entirety of knowledge.
The new baby can now come into this earthly plane and live and grow in this world with all its earthly limitations and possibilities. The philtrum serves as a lifetime reminder of what was once known, what must be learned, and what will one day be known again.
— Wayne Dosick, Soul Judaism