One very sly argument I have seen many Protestants make over the years is to quote Jesus' words in Matthew 5:48, "You must be perfect as your Heavenly Father is perfect," and claim that the only way we can be as perfect as God is by having Christ's perfect Righteousness imputed to us. This post will show why this Protestant argument is simply desperate and exegetically bankrupt, being one more proof that the Protestant understanding of Salvation is flatly unbiblical and leaves them grasping at straws.
The first place I want to look at is the term "perfect," which is the Greek term teleios. This term comes from the Greek word "telos," referring to something reaching it's end-goal or fulfillment. It doesn't refer to perfection in the sense of being without any flaws, any weakness, any sins, etc. The way the term is typically used, it refers to a maturity of being. For example, Jesus tells the rich young man, "If you will be perfect, go and sell all you have..." (Mt 19:21). Clearly, Jesus was not saying selling possessions makes someone perfect, nor was Jesus saying this man was 99% perfect in every way, but rather that to be the ideal Christian the rich young man was called to go beyond just the mere keeping of the Commandments. Many times when Paul uses the term, he is speaking to Christians, telling them to be mature (1 Cor 14:20; Phil 3:15; Col 4:12; Heb 5:14; Jas 3:2), which isn't telling them to have ontological perfection. Given this, the idea that being "perfect" means one is to be sin-free isn't really what the word refers to at all.
Next, we'll look at the logical aspect. Does it even make sense to tell someone to be ontologically perfect in every way just like God? No. Reductio ad absurdum tells us this cannot be what Jesus meant. Jesus wasn't telling us to be almighty, everlasting, etc. The Protestant might object and say this perfection only applies to moral living, but this is simply begging the question and really doesn't help their case, because now they must appeal to context. But even given all that, Jesus could be speaking hyperbolically, meaning He used extreme language to make a point, such as when He says a few verses back if your hand causes you to sin you must cut it off (Mat 5:30). Christian tradition has always been clear that you're not supposed to literally cut off your hand. Nobody ever believed that, and rightly so, because it wasn't Jesus' point. The point Our Lord was making is that we must strive to remove near occasions of sin from our life, be it tv, internet, alcohol, etc. So it can be said Jesus simply meant 'strive to be as perfect as you can in your living,' not meaning literally (absolutely) perfect.
When it comes to context, Jesus is especially concerned with what He just said, recorded in Matthew 5:43-47. In this pericope, Jesus says Christians cannot be like the Pagans who only show love to those who love them in return. Rather, Christians are called to love not just their friends, but also their enemies! This is undoubtedly one of the hardest teachings in the Bible! Jesus explains that God the Father sends rain on the just and the unjust, meaning God treats even evil men with kindness. Jesus begins by saying we must love our enemies in order to be "sons of the Father," and Jesus closes this lesson by saying we must "therefore" (connecting it all together) be perfect as the Father is. In other words, by loving our enemies, we loving in the 'perfect' way God wants us to and the 'perfect' way God loves. Not perfection in the sense of degree, but perfection in the sense of 'type'. True love doesn't discriminate.
To build on this, there is even more context to consider that puts a nail in the coffin for this Protestant argument. First consider the Beatitudes ("Blessed are those") of Matthew 5:2-12 where those doing these good works will be rewarded with Heaven. That sounds like an attainable goal Jesus is giving, meaning He wouldn't be asking for an impossible level of perfection later on. Second, Jesus said in Matthew 5:20 that our own righteousness must be genuine and not like that of showy-righteousness of the pharisees, which again makes no sense if Jesus is trying to teach that we cannot be righteous and instead must rely on an imputed alien righteousness. In the second half of this sermon, Jesus says we must do our righteous deeds with the right motives (Matthew 6:1), which doesn't fit the Protestant idea that we cannot be righteous. And lastly, in Matthew 6:9-15, Jesus teaches us how God wants us to pray, the perfect prayer, including the clause "forgive us our trespasses." Now why would Jesus have us say this if He demanded absolute perfection? This part of the Lord's Prayer shows clearly that we will not be absolutely perfect, but ironically we will be perfect by praying this perfect prayer!
Sadly, many Protestants I've come across think Jesus wasn't being serious when He gave this Sermon on the Mount (Mat 5-7), and rather they say Jesus only said these things to show just how sinful we really are and how we can never really obey these. But we all know better. That's just an excuse because the Sermon on the Mount totally contradicts Protestant theology. This is why you'll almost never hear Protestants preach out of these chapters. Instead, you'll find all kinds of snippets and snide remarks about these chapters. Protestants simply don't know what to do with these chapters because their assumptions regarding salvation by faith alone make nonsense of most of what Jesus taught.
I believe that any fair-minded Protestant will see and be convinced of this case I just made and hopefully never use this "be perfect" verse as a pretext to argue for the unbiblical and dangerous doctrine of Imputed Righteousness of Christ.