John10:30 does say 'GOD and I are one.'
However earlier verses say:
15 As the Father knoweth me, even so know I the Father: and I lay down my life for the sheep.
16 And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd.
17 Therefore doth my Father love me, because I lay down my life, that I might take it again.
18 No man taketh it from me, but I lay it down of myself. I have power to lay it down, and I have power to take it again. This commandment have I received of my Father.
25 Jesus answered them, I told you, and ye believed not: the works that I do in my Father's name, they bear witness of me.
26 But ye believe not, because ye are not of my sheep, as I said unto you.
27 My sheep hear my voice, and I know them, and they follow me:
28 And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand.
29 My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand.
These verse quite clearly show the CONTEXT: That Jesus is explaining GOD has tasked him with helping the lost sheep escape the wolves of the temple.
By saying GOD has to lay down his life we have to wonder who raises Him on the third day as presumably with GOD dead on the cross Jesus must also be dead and the holy spook too.
So many people cannot read a full chapter to determine the context and understand who is speaking and from whom to who do the words apply.
For instance, Exodus 3:2 clearly explains how an angel can speak for GOD and be taken as GOD's representative.
2 And the angel of the Lord appeared unto him in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed.
3 And Moses said, I will now turn aside, and see this great sight, why the bush is not burnt.
4 And when the Lord saw that he turned aside to see, God called unto him out of the midst of the bush, and said, Moses, Moses. And he said, Here am I.