The Sunday after Pentecost is Trinity Sunday.
We traditionally use this week to consider how our amazing God functions in a Triune manner - one God, three Persons; Father, Son, and Holy Spirit.
For our Synodical stance on the Trinity, click here.
...if that's not 'heavy' enough reading for you, work your way through the Athanasian Creed as is the custom for Trinity Sunday. The Wikipedia Article on the Athanasian Creed is actually pretty decent if you want a brief intro as well...
For a preview of the readings for this weekend, click the links below: