Jesus exhorts us to be perfect in many ways and in different connotations, denotations, and meanings. Obviously, no one is perfect but God, so that can not be what He meant. There are different interpretations of what "perfect" means, such as complete and mature or without fault or blemish or flaw. The elder is to above blame for instance. Pelagius was a heretic that debated St. Augustine and insisted that since God commands perfection, it must be possible, and taught what was known as sinless perfectionism. This is now called "entire sanctification" or perfectionism. It is said by Catholics that saints and the Pope have attained this level of holiness. We are to bear with each other's faults. Eph. 4:2
But God admonishes us not to think of ourselves as holier than thou (cf. Isaiah 65:5). What is commonly understand by the standards of achievement for the believer is that perfection is the standard, but direction or effort is the test. Let me give you an example from the Old Testament. After Israel had received the Law, they told God, "We will do all that is written..." They should have realized that no one can keep the Law but God and should have begged for mercy and grace. Christianity is not a rule book or to-do list or list of dos and don'ts. It is a relationship and Paul even claimed, "not to have laid hold of it yet." Phil. 3:12
Do I need to point out verses that say we cannot attain sinless perfection: 1 John 1:10 says if we claim to be without sin, we make Him a liar and the truth is not in us. Eccl. 7:20 says "Surely there is not a man on earth who does what is right and doesn't sin." and Proverbs 20:9 says "Who can say, 'I have kept my heart pure, I am clean and without sin?'" Psalm 119:96 says there is a limit to all perfection. The point is that we are not saved by performance, but by faith alone and the Law was not given to be a way of salvation, but to measure us. It was given to show no man can keep it! "It is indeed the straightedge of the Law that show us how crooked we really are." Romans 3:20
If we keep the whole Law and offend in one point, we are guilty of breaking it all. What I'm saying is that no one keeps the Law without fault except Jesus and we all fall short and to try to put yourself under it makes you obliged to the whole of it. We cannot attain to God's standards until we reach glory and no longer have the old sin nature or sin virus we inherited from Adam. We not only have broken one of the laws but the whole of the Law and cannot keep it! We all fall short of God's glory. Justification means that God reckons us as just, not that we are just. He calls us just in His eyes; we are both sinners and just at the same time (cf. Gal. 2:17). God no longer counts our sins against us! (cf. 2 Cor. 5:19). Christianity is not about "Do!" but "Done!" It is a done deal. Soli Deo Gloria!