Passage
if these things ye have known, happy are ye, if ye may do them;
if these things ye have known, happy are ye, if ye may do them;
John 13:15 `For an example I gave to you, that, according as I did to you, ye also may do;
John 13:16 verily, verily, I say to you, a servant is not greater than his lord, nor an apostle greater than he who sent him;
John 13:17 if these things ye have known, happy are ye, if ye may do them;
John 13:18 not concerning you all do I speak; I have known whom I chose for myself; but that the Writing may be fulfilled: He who is eating the bread with me, did lift up against me his heel.
John 13:19 `From this time I tell you, before its coming to pass, that, when it may come to pass, ye may believe that I am <FI>he<Fi> ;
The verse centers on "things", "known", and "happy". It is saying that the verse draws attention to "things" and "known", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 16's "verily verily I say to you a..." into verse 18's "not concerning you all do I speak...", so "things" and "known" 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 "things" and "known" with trust shaped by these words, not by a vague optimism outside the passage.