Micah 4:8 And thou, O tower of the flock, the strong hold of the daughter of Zion, unto thee shall it come, even the first dominion; the kingdom shall come to the daughter of Jerusalem.
Migdal Eder was the watchtower that guarded the Temple flocks which were being raised to serve as sacrificial animals in the Temple. The shepherds who kept them were men who were specifically trained for this royal task. They were educated in what an animal that was to be sacrificed had to be, and it was their job to make sure that none of the animals were hurt, damaged, or blemished (Alfred Edersheim in “The Life and Times of Jesus The Messiah”, p. 186-187).
There Jacob fed his sheep Gen. 35:21, and there the shepherds, keeping watch over their flocks by night, saw and heard the Angels singing, “Glory to God in the highest, and on earth peace, good will toward men.” The Jews inferred from this place that the Messiah should be revealed there.
8 And there were in the same country shepherds abiding in the field, keeping watch over their flock by night. 9 And, lo, the angel of the Lord came upon them, and the glory of the Lord shone round about them: and they were sore afraid. 10 And the angel said unto them, Fear not: for, behold, I bring you good tidings of great joy, which shall be to all people. 11 For unto you is born this day in the city of David a Saviour, which is Christ the Lord. 12 And this shall be a sign unto you; Ye shall find the babe wrapped in swaddling clothes, lying in a manger. 13 And suddenly there was with the angel a multitude of the heavenly host praising God, and saying, 14 Glory to God in the highest, and on earth peace, good will toward men.
Jesus’ birthplace was in the traditional location for Passover lambs to be born, since He became the Passover Lamb of God who took away the sins of the world. The shepherds knew where to go to find the newborn babe — and why it being wrapped in swaddling clothes would be a significant clue. Those special shepherds were notified as it was their holy calling to certify Passover lambs upon birth.
However, the traditions of Mishnah (oral Torah – Rabbinic literature) cannot be accepted unconditionally; if there is a Biblical basis, then the tradition is valid.