“Behold, an hour is coming, and has already come, for you to be scattered, each to his own home, and to leave Me alone; and yet I am not alone, because the Father is with Me.” John 16:32 NASB
Although all his disciples would scatter, when He, the Shepherd, was struck, the Lord says that even then He would not be alone, because the Father would be with Him. Now this shows that the Father is a distinct person from the Son; for were the Father the same person as the Son, under simply a different mode, manifestation, or name, the Son would not be able to say something like this. For in that case, the Father being with the Son would mean nothing beyond that the Son would be with Himself; and that this would indeed be to be alone. Yet the Son says that He will not be alone; which manifestly testifies that there will be another with Him; and we are told that this other is the Father. This passage proves then that the Son and Father are distinct from one another, as one person from another. And so the Son was not alone, because another person, the Father, was with Him.
This refutes the false teaching of modalism, which says that the Son and Father are but one and the same person, under different modes, manifestations, or names; for it is seen that there are two really existing persons here, distinct from one another, the Father and the Son. And those so-called trinitarians who believe that the Father and Son are numerically, or individually, one substance or being, run into the same problem; for if the Father and Son are numerical one individual being, then the Father, being the very same being as the Son, can hardly be rightly reckoned to be another, since He is numerically the same individual as the Son, in their view. For they teach that the Father is the whole Supreme Being, and the Son is that same whole Supreme Being; not in part, but each being the entire and whole Supreme Being. Each then being equated to the Supreme Being, will be equated to one another, then, as surely as it holds true that is F=G, and S=G, then necessarily, F=S (F=Father, S=Son, G=the one individual being They are supposed to share). This distinction, then, between the Father and Son seen in this passage, refutes there error as well.
And so the truth stands that the Father and Son are two distinct persons, that is, two distinct rational individual beings; the Father truly Father of another, the Son truly Son of another, so that, being together, each person may truthfully said to not be alone.