“Philip said to Him, “Lord, show us the Father, and it is enough for us.” Jesus said to him, “Have I been so long with you, and yet you have not come to know Me, Philip? He who has seen Me has seen the Father; how can you say, ‘Show us the Father’? 10 Do you not believe that I am in the Father, and the Father is in Me? The words that I say to you I do not speak on My own initiative, but the Father abiding in Me does His works. 11 Believe Me that I am in the Father and the Father is in Me; otherwise believe because of the works themselves.” John 14:8-11 NASB
Here we see at once the unity and the distinction between God and His Son declared. The unity, in that the Son is the Image of the Father, and like the Father, is such a way that to have seen the Son, is to have seen the Father; inasmuch as to have seen an image of something, is to have seen that thing through its image. For we know that “He is the image of the invisible God” (Col 1:15 NASB), to Whom God said, “Let Us make man in Our image, according to Our likeness” (Gen 1:26 NASB), so revealing that the Son and Father share one image and one likeness; which is so well represented in the Son, that to see the Son, is to see the Father through Him. The distinction between the persons is seen from this as well; for in the Son being the Image of the Father, we see His distinction, in that the Image, and the Original pictured in the Image, must be two distinct things; or else one could not be said to be the Image of the other. For one is the invisible God, Who no one has ever seen in His own person; the other the Image of that Invisible God, through Whom He is beheld. And so it will appear obvious that the Sabellian, or modalist, interpretation of these verses, which is to say that the Father is seen in the Son because They are one and the same, is impossible, and inconsistent with what the rest of scripture says on this point.
We also see the close relational unity between God and His Son, that the Father is in the Son, and the Son in the Father, in verses 10-11. But in this description of their close unity, we still see the distinction between the persons, in that were the Father and Son not truly distinct, it could never be said that one was within the other, and the other within the one, since, if each were numerically one and the same individual, this would be saying nothing beyond that one individual dwells within itself, as all do. But for one to dwell in the other, and the other in the one, each must be distinct, so that there is a real mutual indwelling of each person within each other. And so we see that although the Son is in the Father, and the Father in the Son, the Father is not the Son, but They are two distinct persons, or two individual beings.
And so we see this rich passage reveals to use both the unity and the distinction between God and His Son; the Son imaging the invisible Father, and sharing His likeness, and dwelling in Him and the Father in He; yet not, as the modalists say, causing by this any confusion of persons, but rather revealing that, and only making any sense if, each person is truly distinct from the other.