"The altar server has a privileged place in liturgical celebrations.
Those who serve at Mass present themselves to a community.
They experience from close at hand that Jesus Christ is present and active
in every liturgy......
Therefore in the liturgy you are far more than mere 'helpers of the parish priest."
Above all, you are servants of Jesus Christ, the eternal High Priest.   
Thus you altar servers especially are called to be young friends of Jesus."
(USCCB, Altar Servers, Servants of Jesus)