One angel cannot have two missions. "Two angels cannot have the same mission." (Targum Rashi on Genesis 18:2; Bereshit Rabbah 50:2)
This is echoed in physics, where it states "No two objects can occupy the same space at the same time. It is not a repetitive universe, and no situation can re-occur in exactly the same configuration.
We might spend a lot of our time and energy trying to recreate an event that affected us from the past, but even if we repeat it, it will never be the same as the previous one. The classic example of this is sex. If one's first sexual experience is blissful and fulfilling, one will begin to see this bliss in further sexual experiences, but it will never be the same as that first one.
The negative version of this is that the experience is horrible, and so one will spend the rest of one's life avoiding this experience so as not to experience that horror again.
Metatron, the angel
An angel meets Metatron (or a Metatronic event) and it emerges in to our reality – even if only as a momentary and visceral event. It is like the double helix of the DNA molecule. However the angel is not one of the two strands, but the energetic force of the axis mundi around which the two streams, masculine and feminine, form. It is represented by the central column in Kabbalistic thought. Once again, it is not the column itself, but the energy, the space, that "holds" or maintains the column.
From the principle that states: "In order for anything to exist, there has to be the space in which it can exist. So before existence emerged, there needed to be space into which it could manifest. That "space" was fashioned by time! Not the time we measure, which requires already space for the object to be measured in, but time as in the emergence of the finite within the infinite.
We might think of this space as an expansion, but that is from a finite point of view. From the standpoint of the Divine, the space is a contraction.
The angelic force enters via the 10 gates and has to pass through each in order to incarnate (even for a moment). But once ensconced, it forms the link between the upper and the lower worlds of the body and the soul as an expression of the Divine Will to incarnate.
Driven by the desire for the infinite as One, the Unity, to have the only experience it could not have—that of seperateness, of duality, of death. And in the realm of the One as Infinite, there will be the need to express this anti-thesis of Its own Being in some part of Itself.
Notes
Genesis 18:2
ב וַיִּשָּׂ֤א עֵינָיו֙ וַיַּ֔רְא וְהִנֵּה֙ שְׁלשָׁ֣ה אֲנָשִׁ֔ים נִצָּבִ֖ים עָלָ֑יו וַיַּ֗רְא וַיָּ֤רָץ לִקְרָאתָם֙ מִפֶּ֣תַח הָאֹ֔הֶל וַיִּשְׁתַּ֖חוּ אָֽרְצָה:2. And he lifted his eyes and saw, and behold, three men were standing beside him, and he saw and he ran toward them from the entrance of the tent, and he prostrated himself to the ground.
Rashi's commentary
והנה שלשה אנשים: אחד לבשר את שרה ואחד להפוך את סדום ואחד לרפאות את אברהם, שאין מלאך אחד עושה שתי שליחיות. תדע לך שכן כל הפרשה הוא מזכירן בלשון רבים (פסוק ח) ויאכלו, (פסוק ט) ויאמרו אליו, ובבשורה נאמר (שם י) ויאמר שוב אשוב אליך... ורפאל שרפא את אברהם הלך משם להציל את לוט, הוא שנאמר (שם יז) ויהי כהוציאם אותם החוצה ויאמר המלט עלand behold, three men: One to bring the news [of Isaac’s birth] to Sarah, and one to overturn Sodom, and one to heal Abraham, for one angel does not perform two errands (Gen. Rabbah 50:2). You should know that [this is true] because throughout the entire chapter, Scripture mentions them in the plural, e.g., (below verse 8): “and they ate” ; (ibid. verse 9): “and they said to him.” Concerning the announcement, however, it says (ibid. verse 10): “And he said: I will surely return to you.” ... And Raphael, who healed Abraham, went from there to save Lot. This is what is stated: “And it came to pass when they took them outside, that he [the angel] said, ‘Flee for your life.’” You learn that only one acted as a deliverer.
Bereshit Rabbah 50:2
תָּנָא אֵין מַלְאָךְ אֶחָד עוֹשֶׂה שְׁתֵּי שְׁלִיחוֹת, וְלֹא שְׁנֵי מַלְאָכִים עוֹשִׂים שְׁלִיחוּת אֶחָת, וְאַתְּ אֲמַרְתְּ שְׁנֵי, אֶלָּא מִיכָאֵל אָמַר בְּשׂוֹרָתוֹ וְנִסְתַּלֵּק, גַּבְרִיאֵל נִשְׁתַּלַּח לַהֲפֹךְ אֶת סְדוֹם, וּרְפָאֵל לְהַצִּיל אֶת לוֹט