Why do parents love their children? Because the lower world reflects the higher world. And above, there is a Parent and He loves His children.
Why do parents of an only child have such unbounded love for their child? Because this is the truest reflection of the world above: Above, each one of us is an only child, and His love to us is unbounded.
Torat Menachem 5745, vol. 2, p. 1121. Ibid., vol. 3, p. 1725