I think that Jesus is intentionally referencing Isaiah 61 in the opening lines of the Sermon on the Mount.
Isaiah 61 talks about the promised restoration of those who have been loyal to God despite their nation’s disloyalty. They are the oppressed and neglected poor of Israel, but God promises them justice and says he will make them special bearers of his image, turning them into the leaders of his restored Kingdom on Earth.
Jesus in the sermon on the mount picks up very similar themes- he is essentially declaring that in his kingdom the hope to the poor and oppressed will be found!
Behind both of these messages is a recognition that part of what it means to be loyal to God is to recognize that every person in some sense carries the image of God.
Unlike many ancient societies who saw their political and religious leaders as the only ones who represented God, the only ones with the divinely inspired ability to express God’s will to the rest of the world, the God of the Bible has bestowed on all humankind his image (remember, the Hebrew word “Adam” is not just the name of the first man, it means “humankind”). Though people are predominantly idolatrous, giving up their place as the representative of God to serve false idols, there is still a sense in which we all represent God and his character.
So there is a common dignity that we are obligated to give to everyone, especially those that the rest of society has forgotten or neglected. We as those who follow God loyally are called to be the ones who care for the homeless, fight for justice, work to feed the hungry.
And on an even more immediate level, we are to be the ones who make an effort to reach out to and care for the people we see everyday that everyone else seems to forget about or push around. The guy who gets his lunch tray knocked over or his books strewn across the hall. The little freshman that the captain of the varsity squad wants to push around. If we truly believe that all people carry the image of God then we are going to stand up for and reach out to these people.
I’m not claiming this is necessarily an easy thing to do. Neither did Jesus or Isaiah. But if we say we believe one thing and do another we are creating in ourselves a contradiction. As Jesus goes on to say in his sermon, its as if we are a “light” that doesn’t “give light.”