I heard about a pastor who gave someone a stick and asked them to break it. Then two sticks together, then three. By the time it got to four, it became a bundle and was nearly impossible to break.
Paul told the Romans:
"I urge you, brothers and sisters, to watch out for those who cause division and put obstacles in your way that are contrary to the teaching you have learned. Keep away from them." Romans 16:17
Satan wants to lead us astray so he can easily break us by ourselves. But if we unite with other believes, like the bundle, we become unbreakable.