1)
Why is he called "Avdi"?
1.
Radak: You are prepared to go on My missions, like a servant. You said, "here I am - send me!" (6:8)
2.
Malbim: Hashem prepared me for this Avodah (Nevu'ah).
2)
Why does it say "[Yisrael] Becha Espa'er"?
1.
Yuma 86a: If a person learns Torah, serves Chachamim, and deals nicely with people, they cherish those who learn.
2.
Radak: Yisrael refers to the Klal (the entire nation), and also individuals.
3.
Malbim: I (Yeshayah) am glorified to be called Hashem's Eved only when you are at the [high] level of Yisrael. My Avodah was to make you repent. If you will not, I did not succeed; my Avodah was not completed.
