What did Paul mean in 2 Corinthians 6:11 when he said his heart was enlarged toward the Corinthians?

Paul meant his heart was enlarged toward the Corinthians as an open pouring out of his innermost being. He was not restricting them; rather, they were straitened in their own innermost being. He urged them to be enlarged too, that is, to have the same kind of spiritual relationship with him.

Les explains that in 2 Corinthians 6:11 Paul is pouring out his innermost being, even though he writes by inspiration. Paul says their mouth is open and his heart is enlarged. The Corinthians were not straightened in Paul, but straightened in their own innermost being. Paul then speaks as unto his children, urging them to be enlarged also, meaning they should have the same kind of spiritual relationship. The surrounding verses command believers not to be unequally yoked with unbelievers, because God wants separation from the world, just as He separated Israel from Egypt.

2 Corinthians 6:11

O ye Corinthians, our mouth is open unto you, our heart is enlarged.

What was the spiritual condition of the Corinthian church that Paul was writing to?

The Corinthian church was spiritually immature—babes in Christ and carnal. Though the gospel had taken hold enough to bring them out of paganism and they had separated from their pagan background to a degree, they remained carnal and had a long way to go in spiritual growth.