The truest meaning of the word apostle is one who is sent. This is what happened at Pentecost, the disciples were moved beyond the walls of the upper room where everything was safe. It doesn't get any safer telling the story of Jesus to a bunch of people who already know the story (they were there - duh!). The power of the Holy Spirit literally moved the disciples into the streets of Jerusalem AND empowered and equipped them to speak to people in their own languages. This movement is distinguished, unique. It makes followers of Jesus into ones sent into the world. In other words, disciples become apostles when they move out into the world to proclaim the Good News of Jesus Christ. We all are apostles in one form or another. Yet the gift of Apostleship is unique as well.
"From the Greek apostolos meaning "one who is sent out." Apostles are visionary and pioneering, always pushing into new territory. They come with new, innovative means to do kingdom work." _Mike Breen and Steve Cockram "Building a Discipleship Culture"
Given the state of the church at Pentecost I'm kinda grateful for this gift. Breen and Cockram go on to say the core question of Apostles is: Are we leading the people of God to their destiny?