I never heard of S. D. Gordon until doing a tiny bit of research on number 24 of azquotes.com's list of "Top 25 Jesus Quotes."
Gordon was born in 1859 and died in 1936 after a life of Christian speaking, writing, and missionary work. He published over 25 devotional books, most of which were part of his "Quiet Talks" series (e.g., Quiet Talks on Prayer, Quiet Talks about the Tempter, Quiet Talks on Power, etc.).
It's only a guess, but I'm thinking today's featured quote is probably from his book, Quiet Talks about Jesus, published in 1906.
Jesus is God spelling Himself out in language that men can understand.
I'm happy to report there are Scriptural references to back up S. D. Gordon's assertion:
Matthew 1: 23 - The virgin will conceive and give birth to a son, and they will call him Immanuel (which means “God with us”).
John 14:9 - [Jesus talking] Don’t you know me, Philip, even after I have been among you such a long time? Anyone who has seen me has seen the Father.
* * * * * * *Truth is...even though I agree with Gordon's quote, I have to admit that there are still things about Jesus that I don't completely understand. But you know what? I think that's part of the plan. If our minds could totally explain Yahweh, he wouldn't be much of a God, now would he?
For more on the inability to understand Jesus, featuring a Rich Mullins song, take a look at this post from 2015.