1 Corinthians 16:3

And when I come, whomsoever ye shall approve by your letters, them will I send to bring your liberality unto Jerusalem (KJV)

Then: Paul announces both his intent to come wants to be able to talk with a pre-appointed travel team. There were no banks then. The designated carriers will have the money in high value coins, find a way to strap them to their person and travel all the while hoping not to be robbed, hurt, etc. Baker (241) also adds that the Corinthians would then have a personal contact in Jerusalem at the same time the recipients could be aware of Gentile, non-Jewish, believers.

Now: People like to give money when they know the extent of the need and have personal knowledge of the recipients. They also like to share in the joy of bringing new believers into the church universal. Missionaries receive better, long-term support when they schedule intermittent reports and visits with church groups. This is easier done for local missions, but is still necessary for foreign missions.

Extra Source: Cornerstone Biblical Commentary 1 Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.