At Isaiah 43, the people were chastised because they had witnessed YHWH yet they had remained defiant. Hence they were being punished. So the "witness" referred to their having seen (witnessed) YHWH's goodness, but they were condemned because they had failed to respond accordingly. At least, that was the story being put out by the scribes who wished to create a benefit for their (monotheistic) cause.
Secondly, the concept of "name" went far beyond a sound or a written text. To them, a "name" was a person's very being. Hence the need at times for a person's name to be changed (Simon=>Peter, etc., etc.)
Thirdly, the name "Jesus" is a Latin distortion of "Yeshua", which in English would be rendered as "Joshua". A study of the Hebrew person named Joshua should be instructive.
As I have previously stated, I find the concept of a spirit being crawling into Mary's egg and emerging as a "human" beyond belief. I suggest that prior stories in their mythology of angels having sex with women is relevant.