This is near the beginning of Jesus’ ministry. Later on, perhaps, the disciples would be more accustomed to Jesus’ mixing with all sorts of unexpected people! Even now, however, something about Jesus stopped them asking him why he should choose to speak to this person: a woman and a Samaritan! Jesus had a natural authority and presence which was beyond being questioned by the disciples.
The disciples spoke of material food. Jesus pushed the conversation a step further and said that what was food for him (i.e. what gave him life and without which he could not live) was to do his Father’s will.
Because Jesus has come into the world the harvest of the Last Judgement is imminent. Jesus’ very presence brings judgement because people must either accept or reject him; they must choose light or darkness. The Samaritans chose to accept Jesus: this was an unlikely harvest in Jewish eyes, but we have already been told that God so loved “the [whole] world” (excluding none!).