14 “Verily, verily, I say unto you.” Again He returns to the resurrection of souls, that by continual repetition we may apprehend His meaning; because we could not keep up with His discourse hastening on as on wings. Lo, the Word of God lingers with us; lo, it does, as it were, dwell with our infirmities. He returns again to the mention of the resurrection of souls. “Verily, verily, I say unto you, Whoso hears my word, and believes Him that sent me, has eternal life;” but has it as from the Father.
“For whoso hears my word, and believes Him that sent me, has eternal life” from the Father, by believing the Father that sent the Son. “And shall not come into judgment, but is passed from death to life.” But from the Father, whom he believes, is he quickened. What, dost Thou not quicken? See that the Son also “quickens whom He will.” “Verily, verily, I say unto you, That the hour comes when the dead shall hear the voice of the Son of God, and they that hear shall live.” Here He did not say, they shall believe Him that sent me, and therefore shall live; but by hearing the voice of the Son of God, “they that hear,” that is, they that obey the Son of God, “shall live.”
Therefore, both from the Father shall they live, when they will believe the Father; and from the Son shall they live, when they will hear the voice of the Son of God. Why shall they live both from the Father and from the Son? “For even as the Father has life in Himself, so also has He given to the Son to have life in Himself.”
Source: Tractates on the Gospel of John (New Advent)