אַתֶּ֤ם עֵדַי֙ נְאֻם־יְהוָ֔ה וְעַבְדִּ֖י אֲשֶׁ֣ר בָּחָ֑רְתִּי לְמַ֣עַן תֵּ֠דְעוּ וְתַאֲמִ֨ינוּ לִ֤י וְתָבִ֙ינוּ֙ כִּֽי־אֲנִ֣י ה֔וּא לְפָנַי֙ לֹא־נ֣וֹצַר אֵ֔ל וְאַחֲרַ֖י לֹ֥א יִהְיֶֽה׃ (ס)
Ibn Ezra on Isaiah
Ye are my witnesses, etc. Israel is addressed. And my servant. The prophet.
Rashi on Isaiah
whom I chose. He, too, shall testify that I promised him when he went to Mesopotamia, and I kept My promise.