In the First Reading, from the Book of Genesis, we listen to the call of Abram (later changed to Abraham to signify his new relationship with God) to pick up all of his belongings and family and move to a land he didn't know. His obedience to God’s call is a model for all believers. Abraham became the father of many nations and the Father of the Jewish, Christian and Muslim faiths.
The Second Reading is from St. Paul's Second Letter to Timothy. We hear Paul encouraging Timothy to be strong in the face of hardship. We don't hear what that hardship is, but we know from other writings that Paul is in prison and Timothy is facing difficulties in carrying on with Paul's mission. After exhorting Timothy to be willing to suffer for the Gospel, Paul reminds him of the holiness of life he has been called to and how Christ grants us the grace to live a holy life.
The Gospel Reading is from the Gospel of Matthew. Jesus takes with him Peter, James and John and is transfigured before them. His face shines like the sun and his clothes become white as light. Then Moses and Elijah arrive on the scene and begin to converse with Jesus. Moses represents the Law given on Mt. Sinai, and Elijah represents the Prophets. The message here is if you are faithful and obedient like Moses and Elijah, like Peter and Paul and many others, you will be glorified when you reach heaven.