While a plumb line is a useful tool for DIY projects, the more metaphorical plumb line is beyond useful to essential.
In my prone-to-wander humanity seeking to follow a holy God, I need consistent alignment and realignment.
In high school I spent my freshman year in the band. This means that during football season I had to learn to march. One of the first skills you are taught in marching band is how to walk in parade formation — aligning yourself NOT with the person next to you but with the person walking along the far right of your row. I was taught to ignore the people on either side of me. The only way to make a straight line is for everyone in that row to align themselves with a single person.
If I measure the plumb condition of my heart and mind and life against another person, I will only know how much I am aligned with them. This works about as well as hanging wallpaper based on an already not plumb sheet that’s been stuck to the wall or as marching in formation aligned to your neighbor. Insufficient. Ineffective.
The prophet Amos describes a visionary encounter with the Lord (recorded in Amos 7) where God stands next to a straight wall holding a plumb line and proclaims that He is “setting a plumb line among my people Israel; I will spare them no longer.” This warning of pending judgement–a demonstration of just how NOT plumb Israel’s behavior and perspective is–suggests a plumb line that is external.
Perhaps this is reference to the Law of God or the prophet of God — both instruments that point out the shortcomings of humanity in comparison to the expectations of a holy God. Or it could have been a reference to Jesus Christ himself who perfectly demonstrated what a plumb life looks like.
I’m so grateful that God, in his abundant grace and mercy, provides these external plumb lines for us to help us walk in His ways and His truth. I’m also glad that this is not the end of the story.