"In John 10:30 we read Christ's own words.
He said, "I and My Father are one."
Careful reading of the text in
the English shows that the word "my" 
is in italics, which in the Bible
means that it is a supplied word and is not in the original.
---The nature
of the unity of the Son and the Father is not clear in the English. As
far as the English is concerned, it might mean that God the Father and
God the Son are one person.
---Here is where the reading of the original
Greek text is very helpful. The Greek has three genders: masculine,
feminine, and neuter.
---If "one" were masculine in this text, we would
have the form els (heir). But that is not the case. We find that we have the form iv (hen), which
is the neuter.
---It is hard to show this difference in any English
translation, but the effect is to make it plain that the Father and the
Son are not one person. The unity is one of will and purpose, but not of
person.
Neither can the French and Spanish versions show this
difference, for they have no neuter form for "one."
*But Luther could
show it in the German version, where we read, "I and the Father are one (eins, neuter)." Ministry1937