For I have not spoken on my own authority, but the Father who sent me has himself given me a commandment—what to say and what to speak.
49. For I do not speak from myself. That the outward appearance of man may not lessen the majesty of God, Christ frequently sends us to the Father. This is the reason why he so often mentions the Father; and, indeed, since it would be unlawful to transfer to another a single spark of the Divine glory, the word, to which judgment is ascribed, must have proceeded from God.
We have here the honour Christ not assumed, but asserted, to himself, in the account he gave of his mission and his errand into the world. Probably this discourse was not at the same time with that before (for them he departed, Joh 12:36), but some time after, when he made another public appearance; and, as this evangelist records it, it was Christ's farewell sermon...
Commenting on John 12:44-50
For I have not spoken of myself - I have not spoken for my secular interest: I have not aimed at making any gain of you: I have not set up myself as your teachers in general do, to be supported by my disciples, and to be credited on my own testimony. I have taught you, not the things of men, but the deep, everlasting truths of God.