Jesus says in chapter 5 in the middle of the sermon on the mount:
***You, therefore, must be perfect, as your heavenly Father is perfect
Isn’t that a radically tall order?? What exactly does Jesus mean? And how do we achieve it?
Yes it is a radically tall order. To better understand it’s meaning, let’s look at it’s context.
43"You have heard that it was said, "You shall love your neighbor and hate your enemy.’ 44But I say to you, Love your enemies and pray for those who persecute you, 45so that you may be children of your Father in heaven; for he makes his sun rise on the evil and on the good, and sends rain on the righteous and on the unrighteous. 46For if you love those who love you, what reward do you have? Do not even the tax collectors do the same? 47And if you greet only your brothers and sisters, what more are you doing than others? Do not even the Gentiles do the same? 48Be perfect, therefore, as your heavenly Father is perfect. (RSV)
Note that the context here is speaking of love…to be perfect in loving others. This ties in with other core passages in the Gospel.
Mt 22:36-40 - Where Jesus reduces all of the law and prophets to the two great commandments of: Loving God above all else and loving your neighbor as yourself.
John 13:34-35 - Where Jesus gives the Apostles a single command - to Love one another as he has loved us.
St Paul takes up this view and tells us in 1 Cor 13 that Love is greater than either faith or hope (1 Cor 13:1-13), and he reinforces Love at the totality of the law in Romans 13:8-10 where he says, “Love does no wrong to a neighbor; therefore love is the fulfilling of the law.”
St John in his first letter says that he who knows love, knows God for God is love (1 John 4:7-8)
Remember that Jesus was speaking to Jews in Mt 5, 6, and 7 (the sermon on the mount). He was speaking to them about the Mosaic Law. He was giving them the key to keeping the law. Love is the fulfillment of the Law.
your last question - how do we achieve this? As mere human beings, we cannot, but all things are possible with God. So we rely on God and His grace and then we go forth and do what we are able. In short, we practice what we preach and over time we become more perfected in Love.
Hope this helps.
Peace
James