Many Christians try to be good but always feel inadequate about not being perfect. Let’s take a look at this and get out from under the yoke of this outdated ideal.
For one thing, I believe the word “perfect” in Matthew 5:48 must be translated incorrectly or have been used differently when Matthew wrote it. I have not researched this, but I know the word as we use it today (meaning flawless) stems from a different origin. The etymology is: “Middle English parfit, from Old French, from Latin perfectus, from past participle of perficere to carry out, perfect, from per- thoroughly + facere to make, do -- more at DO Date: 14th century.” This does not sound anything like the way we use the word today. I guess I want to believe there is some mistake, because I do not believe human beings can ever be perfect. How could we, with all of our weaknesses, ever be flawless?
Step2
I see God as perfect, and human beings as “becoming” perfect. We are constantly a work in progress. Of course, we can attain limited perfection in certain isolated things we do at any given moment in time. I may be the perfect Christian during prayer, but I return to my imperfect state when I go back to my imperfect life.
Step3
I also believe that there is God perfection and human perfection. I am therefore limited by my humanity. If God is a block of wood, then we are chips off that block. We will never reach the perfection of God, but we can try to be perfect little chips (if we want to). I say all of this in an attempt to answer your question, because you bring up a very important point, but I am no longer troubled by such passages because I do not believe that every word or phrase in the Bible is to be taken literally. I see language as limited when trying to express the Word of God. It sometimes surpasses our expectations and sometimes lets us down. In my communion with God (through the Holy Spirit) He has told me that it is okay not to be perfect but that I should always try to be better than I was yesterday. There is nothing more damaging than a shame-based perfectionist like myself reading Matthew 5:48 and trying to make it happen in my life. Failure after failure will only break my heart and that is not what Christ wants for me. If others want to take Matthew literally they are free to do so. Of course, you may disagree with all of this. As always, I only speak for myself
Authority 
