Musar su Salmi 91:11

Let us now return to the subject with which we began. Whenever a person performs a mitzvah an angel is formed from it which pleads continually on his behalf. Thus the Sages teach in Midrash Rabbah, Parshas Vayikra (32:6), “If a person did a single mitzvah, he is granted a single angel to protect him. If he did two mitzvos he is granted two angels. As it is written, ‘For He will appoint His angels on your behalf’ (Tehillim 91:11).” The expression “he is granted” indicates that from the mitzvos that the person performed these angels are fashioned to protect him from harm. Come and see an incident illustrating this principle. A certain pious man lived in a small village in which there were no books to be found with the exception of a single volume of the tractate Chagigah. All his life the pious man poured over this text. He lived to a ripe old age and then just before his death the tractate Chagigah appeared to him in the form of a woman. After his death this form went before him and brought him into Gan Eden.

After the דינין and משפטים in this portion have been concluded, the Torah turns its attention to Israel's journey towards the Holy Land with (23,20,) הנה אנ כי שולח מלאך לפניך. "Here I am sending an angel ahead of you." Shemot Rabbah 32,6, quotes Psalms 34,8, חונה מלאך ה' סביב ליראיו ויחלצם, "the angel of the Lord camps around those who fear Him, and rescues them." When man performs a commandment of the Torah, G–d creates an angel to protect that person. When said person performs two commandments, G–d provides two angels to protect him, since we are told in Psalms 91,11, כי מלאכיו יצוה לך לשמרך בכל דרכיך "for He will order His angels (pl) to guard you wherever you go." If a person performs many commandments, G–d gives him half His camp as is written: "A thousand may fall on your left side, ten thousand on your right side, but it (disaster) shall not reach you" (Psalms 91,7). This half of G–ds camp is described in Psalms 68,18, i.e. that "G–d's chariots are myriads upon myriads, thousands upon thousands."