In John 10:30 Jesus says, "I and the Father are one [hen]." Doesn't this show that they are one in essence? Find out in this interesting post by Gerald Sigal.
This statement does not suggest either a dual or triune deity. What John's Jesus meant by the word hen ("one") becomes clear from his prayer concerning the apostles: "That they may be one [hen], just as we are one [hen]" (John 17:22), which means that they should be united in agreement with one another as he (Jesus) is always united in agreement with God, as stated: "I [Jesus] always do the things that are pleasing to Him [God]" (John 8:29).
There is thus no implication that Jesus and God, or the twelve apostles are to be considered as of one essence