Passage
They understood not that he spake to them of the Father.
John 8:27 (KJV)
Nearby Context
John 8:25 Then said they unto him, Who art thou? And Jesus saith unto them, Even the same that I said unto you from the beginning.
John 8:26 I have many things to say and to judge of you: but he that sent me is true; and I speak to the world those things which I have heard of him.
John 8:27 They understood not that he spake to them of the Father.
John 8:28 Then said Jesus unto them, When ye have lifted up the Son of man, then shall ye know that I am he, and that I do nothing of myself; but as my Father hath taught me, I speak these things.
John 8:29 And he that sent me is with me: the Father hath not left me alone; for I do always those things that please him.
Study Lenses
The verse centers on "understood", "spake", and "father". It is saying that the verse draws attention to "understood" and "spake", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 26's "I have many things to say and..." into verse 28's "Then said Jesus unto them When ye...", so "understood" and "spake" belong inside that flow. In John context, the local focus is the identity of Jesus, new birth, eternal life, and belief and unbelief.
A plain takeaway is to answer the verse's own emphasis on "understood" and "spake" with trust shaped by these words, not by a vague optimism outside the passage.