If you have done any study in Revelation, this may be one portion you remember. This is the section written to the church at Ephesus. Here Jesus commends their hard work and perseverance, their standing for righteousness and rejecting falsities. Then the sobering judgment, "Yet I hold this against you: you have forsaken your first love." (vv. 2-3) He then tells them to repent, "and do the things you did at first." (v. 5b)
These were people "working hard" for the kingdom of Christ. They were defending His name, not growing weary in the process. They were probably meeting together regularly, doing all the "good things" that Christians should do. But something was missing.
I actually thought back to early love in my own life. I remember getting constant butterflies in my stomach and not eating as well, hanging on every written and spoken word of the other, waiting with longing to see them again. Distant past?
Similarly, when we first experience the love of Christ--His great grace and forgiveness--it spurs us as young believers to get to know Him more deeply. I think that's what was missing. No longer were they "sitting at His feet" and listening to His heart; rather they were busy "doing" for His name. (see Luke 10:38-42)
He sees the heart and is acquainted with all of our ways. (Psalm 139:1-4)
I, by nature, like to be busy. Oh how I do not want His assessment of me to be, "But you left your first love." May we as believers serve Him in the overflow of fellowship-with-Him and worship-of-Him.