Answer:
Haha just listened to a sermon on this.
Explanation:
In this particular situation, Paul is speaking to heavily religious people that were filling the synagogues. These people loved to argue over the 'minor' things, but never confronted the major issues. One example of this was the practice of circumcision by the Jews. They wanted to force the Gentiles to get circumcised, even though they were already saved. This was a minor thing, but all those minor things did not matter because you were saved. This is what Paul means by majoring in the minors.
Hope this makes sense.