Passage
For hee knewe who should betray him: therefore sayd he, Ye are not all cleane.
For hee knewe who should betray him: therefore sayd he, Ye are not all cleane.
John 13:9 Simon Peter sayd vnto him, Lord, not my feete onely, but also the hands and the head.
John 13:10 Iesus sayd to him, He that is washed, needeth not, saue to wash his feete, but is cleane euery whit: and ye are cleane, but not all.
John 13:11 For hee knewe who should betray him: therefore sayd he, Ye are not all cleane.
John 13:12 So after he had washed their feete, and had taken his garments, and was set downe againe, he sayd vnto them, Knowe ye what I haue done to you?
John 13:13 Ye call me Master, and Lord, and ye say well: for so am I.
The verse centers on "knewe", "should", "betray", "therefore", "sayd", and "cleane". It is saying that the verse draws attention to "knewe" and "should", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 10's "Iesus sayd to him He that is..." into verse 12's "So after he had washed their feete...", so "knewe" and "should" 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 "knewe" and "should" with trust shaped by these words, not by a vague optimism outside the passage.