Read Matthew 5:48. Jesus tell us to be as perfect as our Father in heaven is perfect.
Yes, because this is what we are to strive for. The same is true of other passages in the same Gospel, such as 5:30 where we are commanded that if our right hand causes us to sin, we are to cut it off and cast it from us, lest our whole body be cast into hell because of sin. Christ our God is making a point concerning the ultimate goal of our lives: to be perfect, as our Father in heaven is perfect. This is contrasted in the same section with the imperfect, worldly love of the tax collectors and others who love imperfectly, as they only love those who love them back, and greet only their brethren.
God, however, has a different idea of how we are to be. The Sermon on the Mount, the portion of scripture in which that command is found, is basically a lot of contrasts between people's expectations, modes of living, and understanding of how to live a godly life and the message of Christ our God. Hence He structures parts of it in the format "You have heard it said..., but I say unto you...", to turn people's minds from their previous erroneous/limited understanding to the true understanding and meaning of the holy life, as given directly and perfectly by God Himself, Jesus Christ.
As Fr. Tadros Y. Malaty puts it in his
commentary on the Gospel of St. Matthew:
"In the old times, the Lord forbade His people to resist evil by greater evil. He allowed them this because of the hardness of their hearts. But since we are in the New Testament, He has uplifted us to facing evil not by equal evil, or less, or even silence, but to face it with goodness; thereby uplifting us to the summit of perfection."
The phrase "uplifting us to the summit of perfection" is obviously in relation to what had come before this new way of life, which is by comparison less than perfect, not how we should now be, in this NT world we live in. The understanding of what it means to be perfect as the Father is perfect is similar, as our father HH St. Athanasius the Apostolic wrote in his
Epistle to the Bishops in Africa (a letter of 90 bishops of Egypt and Libya to the bishops of the African continent in defense of the Nicene Creed) that
"we too, albeit we cannot become like God in essence, yet by progress in virtue imitate God, the Lord granting us this grace, in the words, 'Be merciful as your Father is merciful:' 'be perfect as your heavenly Father is perfect'."
This is how "be perfect, as your Father is perfect" is to be understood: in reference to the perfection of life offered in Christ Jesus, by progress in virtue that we imitate the Lord our God by being perfectly merciful as He is, loving as He is, etc.
Remember here what I wrote that you are now taking issue with: that we will never become like He is in
essence (only praise before His throne, never occupying it), only be more, and more, and more, and more (etc.) perfected, in the eternal process of Theosis whereby we are perfected by grace and our participation in Him.
In his treatise on perfection (available
here as a Word document), St. Gregory of Nyssa sums it all up in the concluding paragraph as follows:
In my judgment this is the perfection of the Christian life: the name of Christ which demonstrates all his other names shares in our soul, words and life's activities so that the holiness praised by Paul (1Ths 5.23) may be constantly kept in the entire body, mind and spirit with no admixture of evil. If anyone says that the good is difficult to attain--for the Lord of creation is alone immutable while human nature is mutable and inclined to change--how can a mutable nature realize what is fixed and stable in the good? My response is that a person who does not lawfully strive in a contest cannot be crowned (1Tim 2.5); he would not be a legitimate athlete if an opponent were lacking. Without an opponent there is no crown, for victory against oneself is lacking if there is no weakness. Hence, let us struggle against our nature's mutability as though against an adversary; wrestling with our reason makes us victors not by casting it down but by not consenting to the fall. Man can change not only for evil; if he had a natural inclination only to evil it would be impossible to turn to the good. Now the most beautiful effect of alteration is growth in the good since change to a more divine state is always remaking the man changing for the better. What seems fearful (I mean our mutable nature) can serve as a wing for flight to better things, since it is to our disgrace if we cannot change for the better. No one should lament his mutable nature; rather, by always being changed to what is better and by being transformed from glory to glory (2Cor 3.18), let him so be changed. By daily growth he always becomes better and is always being perfected yet never attains perfection's goal. Perfection consists in never stopping our growth towards the good nor in circumscribing perfection.
You will remember, I hope, our earlier conversation on God being "uncircumscribed" according to traditional Christian theology. The same too applies to our perfection: that it be boundless, as the One we are seeking to imitate is likewise uncircumscribed (hence there is no 'end point' to Theosis; it continues on forever because God is infinite). Hence the command that we be perfect as our Father in heaven is perfect is a
call to Theosis -- that we come to share in our portion of the Lord's kingdom, and indeed in the Lord Himself as He has granted us the ability to do by the sacrifice of His Son, our Lord and God Jesus Christ.
Whereas before such a thing would have been impossible, on account of our great sin which has separated our race from God, with the coming of Christ, His taking and purifying and elevating and blessing of our nature in Himself, by the Holy Spirit and of the Virgin Mary, we may now truly respond to such a call by "never stopping our growth toward the good", as our beloved father St. Gregory puts it above.
In Christ, we are a new creature (2 Corinthians 5:17), and our purpose and responsibility are to be perfect (not merely 'good' or 'better than our enemies'). Following Christ is the way to do that.