The lesson was on John chapter 17 where Jesus prays right before he dies. The first part of his prayer mentions himself. The second part is strictly about his disciples. The third part is for “those who believe in me.” So me. Maybe you. He prayed for us to have complete unity.
The teacher said that we tend to think of unity in one of three ways. Unanimity, which he defined as thinking and doing all the same things. This is when you have to have hair cuts to the right length to truly be a Christian. (That was a church I went to in WVA about 25 years ago.) Union, he defined as groups agreeing to get together for a single purpose. These things are generally something like operating a soup kitchen. Unity, he said, is defined by the chapter. It is when the believers show the world that Jesus is from God and that God loves them. (It's actually what the verse says. Which I hadn't ever noticed.)
So, you don't have to agree on what the Bible says or means to be in complete unity. You don't have to do things together to be in complete unity. All you have to do is let the world know that Jesus is from God and that God loves them. Wow, there's a lot more unity in Christendom than I thought.