What is a plumb line in the Bible?
A plumb line is a tool used by builders and painters to find the true vertical. A plumb bob, typically a pointed lead weight, is suspended from a string and gravity then makes the string hang perfectly straight. Thus, the builder can ensure that the structure he is constructing is erected perfectly true and the painter can use it as a reference line. The plumb line has since been replaced by more modern levels; however, it is still an effective tool.In the Bible, God references a plumb line a few times. In Isaiah 28:16–17 God says, "Behold, I am the one who has laid as a foundation in Zion, a stone… And I will make justice the line and righteousness the plumb line." God says that justice and righteousness are the standard by which His people will be measured. In fact, when God sent Amos to warn Israel about the impending judgment due to their corruption, He said, "Behold, I am setting a plumb line in the midst of my people Israel" (Amos 7:8). This symbolic plumb line is the standard of justice and righteousness with which God's people were to align themselves.
Human behavior in the Bible is often referred to as either crooked or upright. Proverbs 21:8 says, "The way of the guilty is crooked, but the conduct of the pure is upright." A plumb line would expose anything that is crooked. Psalm 119:9 asks "How can a young man keep his way pure?" then answers, "By guarding it according to your word." God's Word is the only true standard we have for assessing our actions. In fact, two verses later the Psalmist says, "I have stored up your word in my heart, that I might not sin against you" (Psalm 119:11). God's Word reveals God's standards. As Paul explained to Timothy it is "profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be complete, equipped for every good work" (2 Timothy 3:16–17). The Word of God reveals the plumb line against which we will be measured.
God calls His people to "be holy, for I am holy" (Leviticus 11:44, 45) and yet, "all have sinned and fall short of the glory of God" (Romans 3:23). While we rely on the Holy Spirit to use God's Word to work in our hearts and for that work to manifest in our actions, we can rest assured that everywhere our lives don't align with God's plumb line we can be "justified by His grace as a gift, through the redemption that is in Christ Jesus" (Romans 3:24). The plumb line of God's standards points us to our need for Christ and His sanctifying work in our lives.
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Truth about Everything Else
