The bible expressly mentioned in St. Mark 16:15 "And he said unto them, Go ye into all the world, and preach the gospel to every creature .
Going into "all" the world is a mandate for all Christians. Let's note that the whole world cannot reached by same individuals. Hence, taking the gospel to reach the unreachable requires finances (sponsorship) but because one had supported does not give one the liberty to stand at bay and not witness Christ to others.
Your work place, market, business, school or anywhere God has placed you is your world that needs to be reached and this can done through how you live (that's our number one selling point as Christians - Christlikenes), then reaching out in words. If Christ is not seen in us, we can't really express it to others.
Some people have taken it as a burden, travelling from state to state and country to country, support them, sponsor them bit do not use this to relent in witnessing Christ to others personally.