A second line follows the verse in recitation and is not from Deuteronomy: blessed be the name of the glory of his kingdom for ever and ever. In most Jewish liturgy it is said in an undertone, and the reason given is a story.
The Talmud, at Pesachim 56a, explains that Jacob wished to reveal the end of days to his sons and the divine presence departed from him; he feared one of them was unworthy, and they answered him with the verse from Deuteronomy, at which he replied with the blessing. Because the line is Jacob's and not Moses', it is said quietly, except on the Day of Atonement, when it is said aloud, the tradition offering various explanations of the exception.
This is a tradition explaining an existing practice rather than a record of how it started. The Mishnah at Yoma 3:8 describes the formula being used in the Temple as the response of the crowd when the high priest pronounced the divine name, which points to its origin as a liturgical response, and the undertone as a post-Temple accommodation.
The first verse has functions beyond daily prayer. It is recited before sleep, it is what a Jew is taught to say at the point of death, and it was said by people going into the gas chambers, which is a fact about it that no account of the text should omit.
There is also a scribal peculiarity: two letters in the verse are written oversized in Torah scrolls, forming the word for witness. The reason is not recorded and the explanations are all later.