Why ask 'who is greatest' right then? Some clues suggest a recent event involving Peter might have stirred the pot.
Matthew 18:1 mentions 'at that time,' and some scholars point to recent events that likely fueled the disciples' question and their internal debate.
The Coin from Peter's Mouth
Just before this, in Matthew 17:24-27, Jesus and Peter had the unique encounter where Peter found the temple tax coin in the fish's mouth. This was a special, almost intimate interaction between Jesus and Peter, highlighting Peter's prominence among the disciples.
The Transfiguration Echoes
Additionally, Peter, James, and John had recently experienced the Transfiguration (Matthew 17:1-8). These 'special honors' given to a select few likely intensified the others' feelings of being overlooked and sparked questions about hierarchy and who held the most important position.
Ambition's Nuances
This doesn't mean Peter was inherently arrogant, nor that the other disciples were purely malicious. It highlights how even perceived favoritism or special roles can trigger human desires for status and recognition within a group, especially when the ultimate nature of the kingdom is misunderstood.