44 Then Jesus cried out and said, "He who believes in Me, believes not in Me but in Him who sent Me.
45 And he who sees Me sees Him who sent Me.
46 I have come as a light into the world, that whoever believes in Me should not abide in darkness.
47 And if anyone hears My words and does not believe, I do not judge him; for I did not come to judge the world but to save the world.
48 He who rejects Me, and does not receive My words, has that which judges him — the word that I have spoken will judge him in the last day.
49 For I have not spoken on My own authority; but the Father who sent Me gave Me a command, what I should say and what I should speak.
50 And I know that His command is everlasting life. Therefore, whatever I speak, just as the Father has told Me, so I speak."
believing in the Son (v. 44) = believing in the Father — total unity.
Him who sent Me (v. 45) — Philip said to Him, "Lord, show us the Father, and it is sufficient for us." Jesus said to him, "Have I been with you so long, and yet you have not known Me, Philip? He who has seen Me has seen the Father; so how can you say, 'Show us the Father'? Do you not believe that I am in the Father, and the Father in Me? The words that I speak to you I do not speak on My own authority; but the Father who dwells in Me does the works. Believe Me that I am in the Father and the Father in Me, or else believe Me for the sake of the works themselves (John 14:8-11).
I did not come to judge (v. 47) — Not at His first coming. His judgment will come at His second coming (verse 48).
reject (v. 48) = displace, don't accept His authority or receive His words. It can be neglect, not just outright rejection.
His words will judge (v. 48) because His words are true.
command (v. 49) = charge, commission
This final public statement by Christ is a summation of His ministry over the previous three years. It may be John's summation of things Jesus said earlier (John 1:18; 5:24; 8:12; 8:19; 9:5; 10:38)
This solemn utterance [vs. 48] of Christ corrects an erroneous conclusion which has been drawn by some Calvinists, who deny the responsibility of unregenerate souls in connection with the Gospel. They argue that because the natural man is devoid of spiritual life, he cannot believe; a dead man, they say, cannot receive Christ. To this it might be replied A dead man cannot reject Christ. But many do! It is true that a dead man cannot believe, yet he ought to. His inability lies not in the absence of necessary faculties, but in the willful perversion of his faculties. When Adam died spiritually, nothing in him was annihilated; instead, he became "alienated from the life of God" (Ephesians 4:18). Every man who hears the Gospel ought to believe in Christ, and those who do not will yet be punished for this unbelief (see 2 Thessalonians 1:7). As Christ here teaches, the rejector of Him will be judged for his sin. — Exposition of the Gospel of John, by Arthur W. Pink, page 287