The beloved apostles reasoning for supporting missionaries. Note: John had the heart of Christ like no other. Paul clearly agrees with John's missions philosophy in the last chapter of Romans.
4 I have no greater joy than to hear that my children walk in truth. 5 Beloved, thou doest faithfully whatsoever thou doest to the brethren, and to strangers; 6 Which have borne witness of thy charity before the church: whom if thou bring forward on their journey after a godly sort, thou shalt do well: