Complex sentence: "I Can Only Imagine" was released in 2001 as the album's lead single and it gained significant airplay on Christian radio formats before crossing over to mainstream formats in late 2003 and into 2004.
Split into simpler sentences: I Can Only Imagine was released in 2001 as the album's lead single. During 2001, it gained significant airplay on Christian radio formats before crossing over to mainstream formats in late 2003 and into 2004.