Based upon what or how come that Mashiach is being viewed as a human being, why can’t Mashiach be a heavenly Shaliach, messenger (angel) or divine being?
Yes, the Moshiach has to be a human being as he has to be a descendant of King David (Rambam Melachim 11:4):
"וְאִם יַעֲמֹד מֶלֶךְ מִבֵּית דָּוִד הוֹגֶה בַּתּוֹרָה וְעוֹסֵק בְּמִצְוֹת כְּדָוִד אָבִיו. כְּפִי תּוֹרָה שֶׁבִּכְתָב וְשֶׁבְּעַל פֶּה. וְיָכֹף כָּל יִשְׂרָאֵל לֵילֵךְ בָּהּ וּלְחַזֵּק בִּדְקָהּ. וְיִלָּחֵם מִלְחֲמוֹת ה'. הֲרֵי זֶה בְּחֶזְקַת שֶׁהוּא מָשִׁיחַ. (אִם עָשָׂה וְהִצְלִיחַ וּבָנָה מִקְדָּשׁ בִּמְקוֹמוֹ וְקִבֵּץ נִדְחֵי יִשְׂרָאֵל הֲרֵי זֶה מָשִׁיחַ בְּוַדַּאי."
Now, if a king should arise from the House of David who is versed in Torah and engages in Commandments, as did David his forefather, in accordance with both the Written and the Oral Torahs, and he enjoins all of Israel to follow in its ways and encourages them to repair its breaches, and he fights the Wars of G-d128, then he may be presumed to be the Messiah. If he succeeds in his efforts and defeats the enemies around and builds the Sanctuary in its proper place and gathers the dispersed of Israel, he is definitely the Messiah.