Ye - the Jews, to whom I have given predictions, verified by the event; and in delivering whom I have so often manifested My power (see Isa 43:3, Isa 43:4; Isa 44:8).
and my servant - that is, the whole Jewish people (Isa 41:8).
believe - trust in.
formed - before I existed none of the false gods were formed. “Formed” applies to the idols, not to God. Rev 1:11 uses the same language to prove the Godhead of Jesus, as Isaiah here to prove the Godhead of Jehovah.