Plesion (G4139) is literally 'the near one' โ someone geographically or circumstantially close. But Jesus radically redefines it in the Parable of the Good Samaritan (Luke 10:25-37): the neighbor is not defined by ethnicity, religion, or proximity โ but by whoever shows mercy. The question 'Who is my neighbor?' becomes 'Who are you being a neighbor to?'
The second great commandment in Leviticus 19:18 โ 'Love your neighbor [LXX: plesion] as yourself' โ is quoted more in the NT than almost any other OT verse. Paul calls it the fulfillment of the law (Romans 13:9; Galatians 5:14). James calls it the 'royal law' (James 2:8). Plesion is not the person next door โ it is every human being who crosses your path with a need you have the power to meet.