The reasoning of John 12.47-50 is this...
The Son's words are what judge us. [12.48]Jesus Christ is our judge.
The Son speaks only the Father's words. [12.50]
...the Father's words judge us.
...the Father is our judge indirectly.
...the Son is our judge directly.
Matthew 16.27: "For the Son of Man is going to come with his angels in the glory of his Father, and then he will repay each person according to what he has done."
Matthew 25.31: "When the Son of Man comes in his glory, and all the angels with him, then he will sit on his glorious throne."
Matthew 28.18: And Jesus came and said to them, "All authority in heaven and on earth has been given to me."
John 5.22,27: "The Father judges no one, but has given all judgment to the Son ... And he has given him authority to execute judgment, because he is the Son of Man."
John 8.16: "Yet even if I do judge, my judgment is true, for it is not I alone who judge, but I and the Father who sent me."
Acts 10.42: "And he commanded us to preach to the people and to testify that he is the one appointed by God to be judge of the living and the dead."
2 Corinthians 5.10: For we must all appear before the judgment seat of Christ, so that each one may receive what is due for what he has done in the body, whether good or evil.
2 Timothy 4.1: "I charge you in the presence of God and of Christ Jesus, who is to judge the living and the dead, and by his appearing and his kingdom..."
Revelation 20.11-12: Then I saw a great white throne and him who was seated on it. From his presence earth and sky fled away, and no place was found for them. And I saw the dead, great and small, standing before the throne, and books were opened. Then another book was opened, which is the book of life. And the dead were judged by what was written in the books, according to what they had done.