Read Matthew 18:15,16. This is the principle at work in this chapter. It headed off a potentially violent confrontation between the tribes. The two and a half tribes from across the Jordan wanted to remind the others that the Lord was their God too. Our true unity is in the Lord our God and not in location or origin.
This is why we need Jesus. Because in Him we have a new covenant, where boundaries are not physical, and all are saved, Israel and Gentile.
Reuben, Gad and Manasseh wanted to remind the other tribes that they too were part of the Lord’s people. So they built an altar.
The rest of the tribes saw the altar, mistakenly, as idolatry.
It’s pretty cool that they were so quick to jump on that, which shows that the generation were wanting to obey the Lord (which we hear about a bit more at the start of Judges).
For us, it’s a good reminder to be careful when jumping to spiritual conclusions. There are absolutes, but our perspectives and motivations and actions can be easily misunderstood from person to person, from church to church, from nation to nation.
And it’s also a wonderful reminder of why we need Jesus.
In Him there is no boundary of living outside of His kingdom. We are His kingdom, from east to west across the entire face of the earth, regardless of physical location.
“Now after John was arrested, Jesus came into Galilee, proclaiming the gospel of God, and saying ‘The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel.'” Mark 1 v14-15
Praise God that we are His people, with Jesus as King, reigning over His kingdom.