People often assume that little if any missionary activity took place subsequent to the first-century apostles until William Carey initiated the modern missionary movement. Such a view is not consistent with the historical record, which is most evident in the contributions of Irish and Celtic missionaries in the fifth and sixth centuries.
Long before Carey received a vision to take Christ to a foreign land, a man responded to his own Macedonian call to Ireland, and from there missionary ventures went from Scotland to Switzerland, establishing centers of evangelization and learning. It started not because of a commission of the church at Rome, but as a response of one individual to the call of God upon his life.
Patrick is very much like William Carey. Just as Carey is said to be the father of modern missions, so Patrick can be said to be the father of medieval evangelical missions. For example, he went to a mission field without a commission from any agency or church, although it seems he may have had the approval of the British church, just as Carey eventually received the approval of the British church of his day. Additionally, Patrick established educational programs to initiate his outreach to indigent people, these taking the form of monasteries. Finally, he spent his entire life in service to those to whom he went.
While these details parallel the missionary efforts of Carey, they are not intended to suggest the two men are linked in any historical way. These similarities are mentioned only to demonstrate that the Irish and Celtic missionary of the fifth and sixth centuries operated in ways that have been proven productive in missionary enterprises since Carey and, therefore, can provide for the modern missionary a more ancient example of missionary methodologies that may be enlightening and instructive.