וְהָיָ֥ה פִֽי־רֹאשׁ֖וֹ בְּתוֹכ֑וֹ שָׂפָ֡ה יִֽהְיֶה֩ לְפִ֨יו סָבִ֜יב מַעֲשֵׂ֣ה אֹרֵ֗ג כְּפִ֥י תַחְרָ֛א יִֽהְיֶה־לּ֖וֹ לֹ֥א יִקָּרֵֽעַ׃
And it shall have a hole for the head in the midst thereof; it shall have a binding of woven work round about the hole of it, as it were the hole of a coat of mail that it be not rent.
Tiferet Shlomo
....THE EDGE FOR THE OPENING etc. The hint here is that one's prayer should always be regarding the bitter exile of the Shekhinah (from which we should be quickly saved). The language from our mouths should be continual prayer regarding the pain of Shekhina's exile.
Rashi on Exodus
והיה פי ראשו AND THE HOLE IN THE HEAD OF IT SHALL BE — the hole of the Robe which is at its top — that is, the opening which serves as a receptacle for the neck,
Sforno on Exodus
לא יקרע, the robe should not have a regular collar and neckline running down the front of the garment open, but it should be round as a ring. The expression יקרע, is applied to vertical openings in a garment or building. The expression occurs in a similar sense in Jeremiah 22,14 וקרע לו חלוני, “provided with narrow windows cut out, etc.”