Isaiah 21:6 Midrash

כִּ֣י כֹ֥ה אָמַ֛ר אֵלַ֖י אֲדֹנָ֑י לֵ֚ךְ הַעֲמֵ֣ד הַֽמְצַפֶּ֔ה אֲשֶׁ֥ר יִרְאֶ֖ה יַגִּֽיד׃

For thus hath the Lord said unto me: Go, set a watchman; let him declare what he seeth!

Read midrashic interpretation of Isaiah 21:6: and classical rabbinic exegesis.