The church at Ephesus had everything going for it, except for one critical flaw: they had left their first love. They resembled the rich ruler in Mark 10:17-21, who ran up to Jesus, knelt down, and asked, "Good Teacher, what must I do to inherit eternal life?" After Jesus listed some commandments, the ruler confidently replied, "All these I have kept from my youth." Yet Jesus responded, "One thing you lack..." Similarly, even though Ephesus defended pristine doctrine, they lacked one thing in the most crucial area; they had forsaken their first love.
Doctrinally, they had dotted every "i" and crossed every "t" with a proper cursive stroke, yet their grammar was flawed. The church resembled the scribes and Pharisees that Christ spoke of in Matthew 23:23. "You tithe of mint and anise and cummin, and have neglected the weightier matters of the law: justice and mercy and faith. These you ought to have done, without leaving the others undone."
Ephesus had overlooked Paul's important words in 1 Corinthians 13:2-3, "Though I have the gift of prophecy, and understand all mysteries and all knowledge, and though I have all faith, so that I could remove mountains, but have not love, I am nothing. And though I bestow all my goods to feed the poor, and though I give my body to be burned, but have not love, it profits me nothing."
The honeymoon was over; they had slipped into the rut of routine rituals, merely going through the motions of saying and doing the right things without the motivating drive of love. They were coasting on the momentum of the past...
To remember is a decisive action requiring a conscious, proactive effort to recall the delight and thrill of a previous dynamic relationship. Our mind and heart tend to be like a leaky pail from which the water eventually drains. As time passes, our memories fade, and our emotions cool. The natural decay stems from having mortal bodies. The nation of Israel in the Old Testament demonstrates forgetfulness. Despite witnessing miraculous acts and receiving divine guidance, they repeatedly drifted into idol worship.
To repent means having a change of heart and mind about something, followed by taking corrective action. One might feel regret for their actions and wish they had not done wrong. That's a good start; however, true repentance goes a step further, requiring an about-face with corrective action.
To return to the first love and the first works requires action. Remembering is an act of the mind, repenting is an act of the will, and returning is an act of action.
Christ also outlined the dire consequence should they fail to take corrective action. He warned, "I will come to you quickly and remove your lampstand from its place," which is understood to mean the discontinuance of the church at Ephesus. God does not hoard defunct lampstands; if something or someone has lost its usefulness, it's disposed of.
Quotations taken from the NKJV