Sts Cyril and Methodius
We must invite our friends and neighbors to “taste and see” the great treasure that is Orthodoxy, for it is our responsibility, as Christians, to reach out in kindness, and with a welcoming smile, when we see strangers enter our temples.
Two Byzantine brothers, Saints Cyril and Methodius, brought Orthodox Christianity to the Slavs in the ninth century. The brilliance of Eastern Orthodox missionary outreach, as opposed to that of the Latin Church, was in the very use of the vernacular. These great saints who became known as the Apostles to the Slavs, left the Slavs with a liturgical language that was understandable to them. The services were not imparted in the Greek language, as though it alone was sacred enough to be used in Divine Worship, but helped them understand their new faith by worshiping in their own language.
http://agapienxristou.blogspot.ca/2013/07/sts-cyril-and-methodius-on-great.html