"Unless I wash you..."
It’s not surprising that the disciples were taken aback when Jesus got up part-way through the meal and started washing their feet. This was a menial task performed by a servant upon the arrival of visitors. So for Jesus to do this so unexpectedly clearly had a particular significance, which they would not understand until “later” (7). Only after his resurrection and the coming of the Spirit would they see that it was essential that he died in order to cleanse them – and us – from our sins (1 John 1:7).
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Peter’s reaction is typical of the human pride which thinks it can save itself without submitting to the cleansing which Jesus freely gives. His insistence is emphatic – “no” and “never” (8a). He thinks (rightly) that Jesus is worthy of honour and so he concludes (wrongly) that his refusal of humble service from Jesus is appropriate.
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But Jesus, in reply, is even more emphatic (8b) – the saving work he is about to do for them is necessary, and to reject it out of pride disguised as honour inevitably prevents us knowing Jesus’s holy presence in our lives. Only afterwards could the disciples understand this. How tragic it is if we who live this side of the cross make the same mistake.