שלח תשלח את האם ואת הבנים תקך לך
The Medrash says “What is the reward for this Mitzvah? If you don’t have children I will grant you children. From where do we know this? As it is written ‘Send away the mother bird’, and in return – ‘and take the children for yourselves’”.
What is the connection between sending away the mother bird and children?
The Sefer Nagid U’Mitzvah relates: The Ari Z”l was once a guest at the home of an upstanding person. As he was about to leave, he asked “How can I honor you for your efforts?” He answered “My wife was once fertile, but lately, she seems to have become infertile”. The Ari Z”l answered “At one time, you had a small ladder in your courtyard. The fowl used to jump on that ladder to get to their water. Your wife asked you to move the ladder. Since then, the birds had difficulty getting their water. Their chirps went up to ה', and since then, your wife has been infertile.” He put the ladder back, and his wife became fertile again.
We see that there is a connection between (not) disturbing birds and children, and this explains the Medrash above.
An additional Medrash says “If you observe the mitzvah of sending away the mother, you bring closer the Final Redemption”. What is the connection?
The Yeshuos Ya`akov quotes the Ari Z”l, who explains the Gamara (ע"ז ט') “Tana D’vei Eliyahu: The world’s lifetime is six thousand years: two thousand years of confusion, two thousand years of Torah, and two thousand years are the days of Moshiach. But due to our sins, what came out of it is what came out (יצאו מהן מה שיצאו)”. The Gemara ע"ז ה') ) also says “Ben Dovid won’t arrive until all the neshamos have completed being in bodies”. This refers to the gilgulim – reincarnations – of souls who have to come back to this world, to correct what they failed in previous incarnations. Most of the souls in the world are reincarnations. This is the explanation of “what came out is what came out” - the soul which came out now is a soul which has already come out. As a result, there are no available bodies for new souls who have not yet descended to this world. These souls are still in the heavens, waiting for their opportunity to descend into a body. Only once all these souls have descended into bodies, and completed their roles, can Moshiach arrive. (End of quote from the Ari Z”l)
This fits in wonderfully with the two Medrashim: If someone merits children due to the Mitzvah of sending the mother, those particular children must have a special soul, one which came directly as the result of a Mitzvoh. As such, these souls are new, fresh souls which haven’t been yet in the world. Since Moshiach can only arrive once all the souls have been in bodies, this soul, who arrived as a result of the Mitzvoh of sending away the mother bird, is bringing the Final Redemption closer!
Tzidkas Yosef, Parshas Ki-Teitzei