Passage
From now on I am telling you before it occurs, so that when it does occur, you may believe that I am He.
John 13:19 (LSB)
Nearby Context
John 13:17 If you know these things, you are blessed if you do them.
John 13:18 I do not speak about all of you. I know the ones I have chosen; but that the Scripture may be fulfilled, ‘He who eats My bread has lifted up his heel against Me.’
John 13:19 From now on I am telling you before it occurs, so that when it does occur, you may believe that I am He.
John 13:20 Truly, truly, I say to you, he who receives anyone I send receives Me; and he who receives Me receives Him who sent Me.”
John 13:21 When Jesus had said these things, He became troubled in spirit, and bore witness and said, “Truly, truly, I say to you, that one of you will betray Me.”
Study Lenses
The verse centers on "telling", "before", "occurs", "does", and "believe". It is saying that the verse draws attention to "telling" and "before", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 18's "I do not speak about all of..." into verse 20's "Truly truly I say to you he...", so "telling" and "before" 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 "telling" and "before" with trust shaped by these words, not by a vague optimism outside the passage.