Passage
At present I tell you, before it come to pass: that when it shall come to pass, you may believe that I am he.
At present I tell you, before it come to pass: that when it shall come to pass, you may believe that I am he.
John 13:17 If you know these things, you shall be blessed if you do them.
John 13:18 I speak not of you all: I know whom I have chosen. But that the scripture may be fulfilled: He that eateth bread with me shall lift up his heel against me,
John 13:19 At present I tell you, before it come to pass: that when it shall come to pass, you may believe that I am he.
John 13:20 Amen, amen, I say to you, he that receiveth whomsoever I send receiveth me: and he that receiveth me receiveth him that sent me.
John 13:21 When Jesus had said these things, he was troubled in spirit; and he testified, and said: Amen, amen, I say to you, one of you shall betray me.
The verse centers on "present", "tell", "before", "come", "pass", and "shall". It is saying that the verse draws attention to "present" and "tell", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 18's "I speak not of you all I..." into verse 20's "Amen amen I say to you he...", so "present" and "tell" 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 "present" and "tell" with trust shaped by these words, not by a vague optimism outside the passage.