This puts it so well:
From Gary Friesen, Decision Making & the Will of God, p.330.
Rather than waiting for some kind of mystical 'call' from God, every believer should respond to the revealed will of God (in Scripture) by giving serious consideration to becoming a cross-cultural missionary.
The command to "make disciples of all nations" was given to the disciples of Christ and remains in effect even until the end of the age (Matt 28:19-20). For the believer, personal involvement in the cause of world missions is not optional. We don't need a call -- we've already been commissioned. Every single Christian is to be making some contribution to the objective of world evangelization and discipleship.
From Gary Friesen, Decision Making & the Will of God, p.330.