I'm a baptist because baptist theology is correct. You are a sinner undeserving of heaven, but the message of the Bible is that you can be saved if you believe on Jesus (John 3:16). This salvation is by faith alone, it doesn't come by performing works such as taking the Lord's supper or being baptized (Ephesians 2:8-9).
As opposed to observing "sacraments", which has connotation to receiving grace through action, we observe the two ordinances of the Lord's supper and baptism. Our name "baptist" comes from our practice of believers baptism by immersion, with no practice of infant baptism. This sets us apart from the state churches throughout the ages who introduced infant baptism, but the Bible only instructs believers baptism and gives no other examples. The word "baptise" even literally means to immerse.
Our highest calling is to follow the great commission by sharing the gospel. We do this because it saves souls, faith comes by hearing (Romans 10:17). We do it because we love our neighbors, local and foreigners.
I am a southern baptist because my church cooperates with other baptist churches to preach the gospel, through the Southern Baptist Convention. The convention is just a way we share resources, it's called the cooperative program. More than half of SBC funds goes to foreign missions, about a quarter goes to local missions (USA), and the rest goes to seminaries and other convention entities. We're also part of a state convention here in the south that operates the same way. None of these groups have authority over our church, we are autonomous because that is the Biblical mode of ecclesiology.
Everything we do is based on what the Bible teaches. The Bible is our only infallible source of authority. On sundays, we sing worship to the Lord, hear a sermon where our Pastor explains a pericope of scripture, we pray together, and we take the Lord's supper. We also have a Sunday School hour where we meet in smaller groups to pray together and work through a different sort of Bible lesson.
