Charles Ellicott Commentary John 12:50

"And I know that his commandment is life eternal: the things therefore which I speak, even as the Father hath said unto me, so I speak." — John 12:50 (ASV)

And I know that his commandment is life everlasting.—i.e., the commission of the Messianic work. It is better to read here, as before, eternal life (Compare to John 3:15 and others). The Son speaks not of Himself, but He speaks as executing this commission, which brings spiritual and eternal life to the world. It could not be otherwise. This commandment being eternal life, the whole teaching of the Messiah must simply be an utterance of it.

As the Father said unto me, so I speak.—This clause answers to “what I should say and what I should speak” in the last verse. The external revelation is regarded as the work of the Son. That which the Father says is the truth revealed, and the matter and form are here identified.