The Trinity as Call to Action

It's often joked that Trinity Sunday is "the preacher's nightmare." But while the Trinity can be viewed as the most arcane and inaccessible Christian doctrine, it's also the most ordinary and obvious. Every Catholic invokes the Trinity whenever he crosses himself in the name of the Father, the Son, and the Holy Spirit. Moreover, every single baptized person has been baptized in the name of the Father, and of the Son, and of the Holy Spirit. Through baptism we've been sealed by the Trinity, brought within its dynamic, and sent out on mission.