This wording by Jesus is often understated. Yet, Jesus is using the strongest possible language.
The Greek word translated here as departed or left is:
ἀφίημι, aphiēmi
According to the NET footnotes, "the word can actually be used of divorce, so the imagery here is very strong."
Did you catch that? Jesus is telling the church at Ephesus that they have great works. We might say in our modern vernacular that they have great theology and doctrine. They don't give up, and they have great discernment.
Yet for all of that, Jesus says that they divorced Him. They are no longer part of the bride.
We can have great sermons, with the Bible taught line by line. We can take a stand against abortion, LGBT issues, and more. We can do and do, yet if the focus isn't Jesus, all the doing in the world be us is meaningless to God.
Jesus must be our primary motivation for everything we do.
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