Brotherly Kindness & Love
Everything that we have been building on the inside is what is meant to reinforce what is on the inside. We are talking about brotherly affection and love. This is what is on the outside. It is the proof of the inner workings when everything is going right. It shows that on the outside things can begin to look and see and perform of what Jesus has done on the inside.
In 2 Peter 1, we're given a list of qualities that followers of Jesus are called to add to their faith. It says, "For if you possess these qualities in increasing measure, they will keep you from being useless or unfruitful in the knowledge of our Lord Jesus Christ." Much like building a house, the foundation of faith is just the beginning. If we want to build something that is meant to last, what we build with matters too.