Pastor John from 1985:
Just as God delights in his own glory by pouring it out in mercy for others to enjoy, so the chief end of man is not merely "to glorify God and enjoy him forever." Rather, this chief end is to double his joy in God by seeing it expanded and deepened as he pours it out in mercy for others to enjoy. Commenting on the Westminster Shorter Catechism ("The chief end of man is to glorify God and enjoy him forever.") [Dan] Fuller says,
This is not quite accurate, for it sets forth only man's penultimate, not ultimate, end. Great indeed will be our joy as we enter into the marvelous fellowship that exists between the Father and the Son. But that great joy will be greatly enhanced as we seek to bring others into the same joy of it. Wolfgang Goethe said, "A shared joy is a doubled joy." Only as we share our joy of the fellowship between the Father and the Son will that joy become a doubled joy. Jesus himself said (Acts 20:35) that "it is more blessed to give than to receive." Man's truly ultimate end, to use the words of Dietrich Bonhoeffer, is to be "a man for others." And the best thing which we can do for others is to get them to experience in their own hearts the love whereby the Father has loved the Son. (Unity, VII-11)
In other words, the call to be a missionary is the call to maximum joy in this world and in the age to come.
Excerpted from A Vision of God for the Final Era of Frontier Missions.