Following men is condemned in the Bible. Many of that time were naming their churches after men such as Paul, Chephas, and Apollos. Paul was telling them that this was wrong because it did not put Christ first and also caused divisions among them. Denominations are unscriptural because they do not require membership for salvation. A big problem with denominations is that they preach contrary gospels.
Denominationalism claims to hold all the saved.
No matter if you are Baptist, Methodist, or Lutheran, you are considered saved. The problem with this is that every denomination has a different creed book, founder, way to be saved, and use of the scripture. Paul then repeats what he said in verse 8 in verse 9 telling us that men will also be accursed if they teach any other gospel. There is only one gospel of Christ and anything else is wrong. Many denominations change their creeds every few years.