I've had quite a bit to do with pagans, ever since the Scottish Pagan Federation asked to be members of Interfaith Scotland. This set the cat among the pigeons and some of the more mainstream religions were very suspicious about it and fearful that it would bring the whole work of interfaith relations into disrepute. The upshot of all this was that we had to talk to pagans and we discovered that they were very nice people, ordinary people like us trying to live a good life, trying to make sense of all that life throws in our way and seeking a faith that would give meaning to their lives. Their faith was centred on a belief in the goodness of creation, on a divinity that could be imaged as both masculine and feminine, and on a way of life that respected the created world, that encouraged an ethical and moral way of life, aware of the interrelatedness of all living creatures and summed up in the dictum "Do what you will, as long as it harms none". Their desire was to engage in dialogue with other faiths, to become known and understood and to work with others for the common good. I'm glad to say they did get membership of Interfaith Scotland but it took a lot of discussion and discernment before that happened.
Originally the word pagan meant one who came from the countryside and is used in both the Hebrew and Christian scriptures for those who were not Jewish or Christian. It distinguished those who belonged from those who didn't, it set 'us' against 'them', it judged the other and the other's religion as inferior. Both Judaism and Christianity discouraged contact with those they regarded as pagan in case they sullied the purity of their religion or even worse attracted converts.
So what is Matthew talking about when he talks about pagans. Is Jesus comparing them unfavourably with those listening to his words? Since this is a community document it's more likely that he's pointing out that it's his listeners that are concerned with material goods and that it's their prayers that are empty. Jesus is exhorting his listeners to trust in God and his words should be read as an exhortation to his followers and not a judgement on pagans. Unfortunately a literal reading of texts such as this has formed a mind set which saw pagans in a negative light and which had repercussions for us in Interfaith Scotland - even into the 21st century.