Live out your God-created identity. Live generously and graciously toward others, the way God lives toward you.
Matthew 5:48 The Message
The Message uses different words than other translations with most expressing verse 48: You therefore must be perfect, as your heavenly Father is perfect. Peterson is likely trying to steer our minds away from a preconceived idea of "perfect". Often we associate being perfect as an impossible goal. In our mind God's perfection is less of a stumbling block, but because of our imperfect and frail humanity we fall short of perfect all the time. So what does Jesus mean when He says you and I "must be perfect"?
Perfect refers to completeness, to a maturity in our character. When we trust Jesus, He defines us, gives us a new identity. The Holy Spirit dwells within us teaching us to become more like Jesus. And Jesus teaches us to live generously and graciously toward others, to love others in His name. Our natures are not so generous or gracious, and we find ourselves imperfect or incomplete without Jesus. Because God loves us with an everlasting love and offers us unmeasured grace, we are to live like Him. Without Jesus, we do not have the ability to live without malice or envy, prejudice or indifference, self-righteousness or injustice. With Jesus, each of us is created new, given a God-created identity. So, become complete with Jesus; love others completely, as God loves! ~ dho