Luke said that the angel told the shepherds that there would be a sign for them (καὶ τοῦτο ὑμῖν σημεῖον) in order to find this baby child (εὑρήσετε βρέφος) that would be a Savior, Messiah, Christ, and Lord. This baby child would be wrapped in bands of swaddling cloth (ἐσπαργανωμένον), lying in a manger (καὶ κείμενον ἐν φάτνῃ). Instead of the sign of a star, as in Matthew, chapter 2:2, they were told about a place with a manger. These shepherds did not bring any gifts with them, unlike the Magi with their gold, frankincense, and myrrh in Matthew, chapter 2:11.
Here there is no doubt as Ezekiel has Yahweh begin and end with this phrase that he, Yahweh, is their God. Therefore they have to follow his statutes, his observances, and keep his Sabbath. The Sabbath has become the sign between Yahweh and his people.