Ask 10 different youth pastors to fill in the blank and you'll likely get 10 different answers. Sometimes they are couched in grandiose mission statements that are so long that no one can remember them. But if you cut through the "catch-phrases," those answers will probably range from retaining students to recruiting students, or from educating students to entertaining students.
And if there's any doubt about how you would fill in the blank, you can set the long statement and the buzz words aside and just look at the calendar, budget, and teaching plan. Your answer will be obvious.
I am convinced that the purpose of youth ministry is faith formation through participation.
This answer keeps us from the false-dichotomies of retaining and recruiting, or educating and entertaining. Faith formation picks up and includes all of these. You've got to add members AND keep them. You've got to instruct them AND make it worth their time. But most importantly, "formation" also captures the unfinished, developing nature of faith - especially in teenagers.
This formation happens through participation, which is another word that can be unpacked. Participation brings together all the various pieces of experiential learning. More particularly, I have in mind instruction, action, reflection, and conversation. Participation happens as you teach students the biblical narrative of God's active presence in the world, coordinate activities that allow their participation in that drama, allow space for them to reflect on what they've seen/heard along the way, and open venues for discussion as they go forward.
With the purpose of youth ministry (faith formation through participation) clearly stated and understood, the youth pastor's job, then, is to create environments, plan activities, and build relationships that work together toward that end.
Today's Learning Is Tomorrow's Teaching
The Work of the Church