For most of my life, I have understood the term "nominal Christian" to refer to someone who claims to be a Christian but who is wholly or mostly absent from religious activities. I now find I need to expand that notion to include Christians who are very, very active in religious activities and, in fact, often adhere to a very punctilious and very conservative form of Christianity, whether Catholic or Protestant evangelical.
I have met more than a few very conservative, highly active Christians whom I now categorize as "nominal Christians," just as nominal as the Christian who rarely, if ever, attends a church service of any kind. As I said, the problem cuts across our Catholic and Protestant evangelical boundaries.
There is an objective, revealed standard of Christian personality: kind, patient, humble. When I meet a missionary, or a person immersed in his religious practices, or one posing as an interpreter and teacher of his religion (whether layperson or cleric), but who, nevertheless, lacks the traits of the objectively revealed Christian personality type, I have no choice but to honestly view that person as a nominal Christian, regardless of his extensive religious activities. Your level of religious participation does not protect you from being a nominal Christian.
First Corinthians 13 always bears rereading by all of us: