Answer: It is written in the Torah, “…in pain you shall bear children.” Spiritual birth cannot take place without pain, so giving birth in our world is painful; this is the root and branch.
Even elementary particles that connect feel pain in the creation of a new connection. Each particle must diminish its influence and obey the opposite particle and thus create a kind of conglomerate, a connection of opposite attributes.
If a new life is created—which means that the transformation becomes you are for me and I am for you, alternately—it turns out that everything is based on painful concessions.
When it comes to the birth of the next spiritual level, it is always painful since you must ascend above yourself, above your ego.
From the Kabbalah Lesson in Russian 1/3/16