The unity displayed by the persons of the Trinity is described as homoousios. This word was first used to describe the Trinity by the Council of Nicaea in AD 325. Homoousios means “of one substance.” This goes much further than to say “of the same variety” or “very similar.” It means more than “identical on the surface,” as some siblings may be. Homoousios means entirely entangled, to the point that it’s impossible for true division to occur. This is the most real, most complete state of unity. Knowing this absolute closeness that has always existed between him and the Father (v. 5, John 17), Jesus expressed the desire that his followers would also be unified in that way (https://www.britannica.com/topic/homoousios).