You remember hearing that phrase from your dad, or maybe your grandfather? Guess what? It's biblical!
Jesus combined two ideas in his teaching that we call the Sermon on the Mount. First, he tells his listeners to "be perfect, therefore, as your heavenly Father is perfect" (5:48). Later, as he concludes his teaching, he says, "[E]veryone who hears these words of mine and puts them into practice is like a wise man..." (7:24).
This last concept is the core of the entire block of teaching. It's the reason the gate to Jesus is so small and the road so narrow--because so few are willing to actually put into practice the teachings of Jesus.
Why do you think Jesus teaches about being salt and light? Why does he teach them the law by saying, "You have heard what the law says, but I say to you"?
It's because his hearers, like us, were accustomed to listening, to acquiring knowledge, but not acting on it. So someone could say, "I haven't murdered anyone, so I'm doing well as a Christian." But Jesus says, "Wrong--if you are angry with a person, you need to fix that relationship."
There's a big difference between avoiding something and being proactive in something. Jesus' teaching is about proactiveness--how else are we going to be salt and light in the world?
As he concludes his teaching, he makes clear that it's about the foundation we build on. His words, and the practice of them, are the solid rock for us to build on. The sit-back, laissez-faire, consumer-consumption approach is the sand that many of us build on.
Let's heed the words of Jesus, aim for perfection, just like our Father, and practice his words.
Practice makes perfect.