I'm Lutheran and he's Baptist

Answer 1

I'm actually in the exact same situation in reverse. I'm a Baptist (affiliated with the Cooperative Baptists) who is dating a Lutheran. I have been doing my research on Lutherian theology in order to understand the similiarities myself.

The first thing you should remember is that your faith is exactly the same.  Any true Baptist will stand with Lutherans in proclaiming that they are saved by the grace of God.  It is God's doing and not our own that saves us. Baptists do not believe that the individual can save him/herself.

This being said, how one is saved might differ, particularly in how much agency the human being has. Luther's are dedicated to the idea that the human being cannot act in being saved. The human being must be passive and allow God to do God's work. Even trust in God is a gift from God. Baptists will agree that one is saved by one's trusting in God but most Baptists will be Armenian in theology. This means that the human being must respond to God's offer of salvation in order to be saved. The end result (trust) is the same but the path differs slightly. I tend to believe that Lutherans are very similiar to Baptists in most of their bliefs in savation.

The other major theological difference between the two is the issue of infant baptism.  Baptists practice "Believer's Baptism" wherein baptism is administered only after the decision to become a christian. The church then is made up of only those who have decided to follow Christ. Baptism is also a symbol of Christ's death, burial and resurection. It does not aid in salvation (the same could be said for Eucharist/communion). Lutherans baptise infants to aid in salvation. Most traditional Baptists will have strong reservations with baptising infants (even though many of us baptise young children) which you will deal with if you have children (particularly with your families). 

Lastly, the source of authority is inportant. Lutherans rely heavily on the tradition of Luther and his reading of scripture. You rely on creeds established by the church to protect against heracy.  Baptists believe in "no creed but Christ." We do not recite creeds and we believe in the individual's ability to make his/her own theological decisions. Granted, Baptists are known for argueing about their disagreements and for breaking into different groups because of these disagreements, but historically we believe in the individual's ability to read scripture and come to his/her own conclusions.

This is a very basic comparison of some of the issues I'm thinking through. More information can be found here:

http://en.wikipedia.org/wiki/Baptist_beliefs