"Person" in
Hebrews 1:3 is not a good translation.
The Greek word is
hupostasis (from whence we get the term Hypostatic Union). It means the concrete substance of a thing, that which make something what it is. This isn't really the best way to define person.
So,
Hebrews 1:3 would be better understood the following way:
(Referring to Jesus) Who being the effulgence of God's splendor, and the exact representation of God's substance (or the physical icon on earth of what God is in Heaven)...
This is born out by the Greek word always used to refer to Jesus as the "Son" of God. The word for Son is
huios (sometimes spelled
iuos). It means bearing the resemblance of another some "thing", so much so, that no discernible differences between the two exist.
Jesus and the Father are one. Christ represents and acts as the Father's agent and ambassador on earth, bearing the very image of His God, so much so, that no discernible differences between them exist.
He that has seen Jesus has seen the Father. But guess what? None of us have ever literally seen Jesus, have we? So I guess none of us have ever seen the Father, then, either.
Not so! The Greek verb to see, as in
John 14:9, while it can literally mean to see, is better understood as meaning, especially in the case of
John 14:9, as to "experience", from the Greek word
horao, to see with the mind, i.e. perceive, to become acquainted with through experience.
John 14:9 then reads "...He that has experienced me has experienced the Father..."
By coming to faith in the Son, we automatically get a relationship with the Father, because the Father is unknowable apart from the Son (See, for example,
Matthew 11:27).
And only the Son can reveal the Father (from
apokalupto, to uncover, open up that which has been veiled, disclose, etc.).
So it's not a revelation that the man Christ Jesus is the Father. That is a conflation. Rather, it's that Christ Jesus, as the only one who can reveal and declare or exegete the Father (see
John 1:18), is therefore the only means whereby one may come to the Father, because the Father was in Him to the fullest extent of His, that is, the Father's being (
Colossians 1:19), so much so, that the Father literally emanated out from within the Son of Man (hence the term "brightness" or effulgence in
Hebrews 1:3), as seen, for example, on the Mount of Transfiguration and also in the vision John had of Christ in
Revelation 1, where the ascended Christ, the Son of Man (
Acts 7:56) sits at the right hand of God (
Mark 14:62), and as the High Priest of our faith, ever lives to make intercession for us (
Hebrews 7:25).