See F B Meyer's related discourse on Mt 5:43-48.

Love (25) (agapao from the noun agape) (Click study of agape) describes an unconditional, sacrificial love, which ultimately is the love that God is (1Jn 4:8,16) and that God demonstrates (see note Romans 5:8) (Jn 3:16, 1Jn 4:9) in its supreme form at Calvary.

Jesus said we are to love our enemies because it shows we are loving like God loves His enemies (see notes Romans 5:6, 5:8, 5:10). Here Jesus adds that when we love like God does, such love distinguishes us from the way the world loves.

Reward (wage) (3408) (misthos) literally refers to pay which is due for labor performed or dues paid for work. Misthos is used in two general senses in the NT, either to refer to wages or to reward, recognition or recompense. In this latter figurative usage, misthos refers to rewards which God bestows for the moral quality of an action, such rewards most often to be bestowed in eternity future.

Jesus associates rewards with giving, fasting and praying, teachings that are dependent upon one's motive (see notes Matthew 6:1; 6:2; 6:5; 6:16) and who receives the glory by those acts (giving, fasting and praying). Note especially future rewards for having suffered for the Name of Christ in this life (see note Mt 5:12; Lu 6:23).

Tax gathers were disloyal Israelites hired by the Romans to tax other Jews for personal profit and were crooks, who most Jews literally  loathed. Matthew himself belonged to this disgusting, despised brotherhood. What is Jesus saying? He is saying "Look, even these despicable tax gatherers loved their own kind! So how will your love show itself distinctive if the only ones you love are your own kind? If you are only showing love to friends, you're no better in loving than the thieving tax collector!" One can just imagine the stir that went through Jesus' listeners when he presented this pithy comparison!

Jamieson comments that...

The publicans (tax collectors), as collectors of taxes due to the Roman government, were ever on this account obnoxious to the Jews, who sat uneasy under a foreign yoke, and disliked whatever brought this unpleasantly before them. But the extortion practiced by this class made them hateful to the community, who in their current speech ranked them with “harlots.” Nor does our Lord scruple to speak of them as others did, which we may be sure He never would have done if it had been calumnious. The meaning, then, is, “In loving those who love you, there is no evidence of superior principle; the worst of men will do this: even a publican will go that length.”

If we treat our enemies as they treat us, we are stooping to their low level. And if we treat them just like tax-gatherers treat those who treat them well, what are we doing that's more than lost men do? What makes us any different from them, if that is all they see? How can we act as salt and light if we respond only the unregenerate men do? Nor should we be satisfied to do what the average professing Christian does.  Jesus "raises the bar" exhorting us to go higher and imitate our Heavenly Father.

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Good For Nothing - I attended a get-together with some people I had pastored 40 years ago when they were in their teens. Several men said their most vivid memories centered around the snowball fights we had after our midweek Bible class. I was glad that at least a few remembered some of the things I had said.

One man reminded me that I once told him to be a "good-for-nothing person." We had been discussing Matthew 5:43-48 when he piped up,

"I'm through going out of my way to be nice to the old people who live next door. I mowed part of their lawn one evening, but the very next day he yelled at me when I ran into his yard to get a football that got away from me. What good do you get from being nice to a person like that?"

In answer to his question, I said, "Jesus wants you to be a good-for-nothing person." He grinned and replied, "I've been called that before." But he got the point.

Being a "good-for-nothing person" by repeatedly going out of our way to be nice to someone who doesn't return even a smile of appreciation isn't easy. But that is what Jesus expects from us. And it becomes easier when we remember His continued goodness in spite of our selfishness and ungratefulness. —Herbert Vander Lugt (Our Daily Bread, Copyright RBC Ministries, Grand Rapids, MI. Reprinted by permission. All rights reserved)

IF YOU GREET ONLY YOUR BROTHERS, WHAT MORE ARE YOU DOING THAN OTHERS? DO NOT EVEN THE GENTILES DO THE SAME?: kai ean aspasesthe (2PAMS) tous adelphous humon monon, ti perisson poieite (1SPAI)? ouchi kai oi ethnikoi to auto poiousin? (1SPAI) (Mt 10:12; Luke 6:32; Mt 10:4,5) (20; 1 Peter 2:20)

See F B Meyer's related discourse on Mt 5:43-48.

The unsaved greet each other so there is nothing distinctively Christian about it. If our standards are no higher than the world’s, it is certain that we will never be very salty salt or clear bright lights.

Dr. Martyn Lloyd-Jones speaks to this call to be distinct (not weird, but distinct) explaining that...

The Christian is the man who is above, and goes beyond, the natural man at his very best and highest... There are many people in the world who are not Christian but who are very moral and highly ethical, men whose word is their bond, and who are scrupulous and honest, just and upright. You never find them doing a shady thing to anybody; but they are not Christian, and they say so. They do not believe on the Lord Jesus Christ and may have rejected the whole of the New Testament teaching with scorn. But they are absolutely straightforward, honest and true... Now the Christian, by definition here, is a man who is capable of doing something that the best natural man cannot do. He goes beyond and does more than that; he exceeds. He is separate from all others, and not only from the worst among others, but from the very best and highest among them.  (Lloyd-Jones, D. M. Studies in the Sermon on the Mount) (Bolding added)

Dwight Pentecost elaborates on loving those other than brethren with a question...

Would you prove before the world you are a child of God? Our Lord says prove it by your care and concern for one with whom there are no emotional ties. Take one outside the family circle or your circle of friends or perhaps even your circle of acquaintances. Love your enemies. To respond to the needs of those who are in your family is to show natural affection. The natural man loves his wife and his children, seeks their welfare, provides for their needs. Such is natural affection. To love those who are in the family of God is only to display a natural affection. To go beyond the bounds of those with whom we are one, and have concern for those who are outside of the family is to display a supernatural affection. Our Lord calls for this in Matthew 5:46-48." (Pentecost, J. D. Design for living: Lessons in Holiness from the Sermon on the Mount. Kregel Publications) (Bolding added)

Jesus command to love and pray for enemies begs the questions...

Is there something "supernatural" about my love, something that cannot be explained in natural terms?

Is there in my love something which is not present in the love even unbeliever's show to one another?

If our answers to these questions is not "Yes" (at least to some degree) then we must each ask ourselves "Why not?"

Jesus' teaching probes and searches deep within our hearts, in those secret places that no one else sees or even knows. We are called to be radically, distinctively different. Salty salt. Bright clear light. The world is in desperate need of seeing such supernatural love without limits and you are the salt that someone needs to taste and the light that someone needs to see today. Let your light shine before men in such a way that when they see the way you love without limits or conditions, they will receive a proper opinion of and be drawn to our Father Who art in heaven.