The term “zealous” describes enthusiasm for the gospel, being hot
for God and a source of refreshment to those around the Laodiceans. Such zeal demands a change of attitude (with resulting behavioural changes) that contrasts with the lukewarmness of Revelation 3:16 and the smug self-sufficiency implied in Revelation 3:17. This radical change in attitude involves repentance, sorrow of heart for their indifferent stance to the gospel.
19 Those whom I love, I reprove and discipline, so be zealous and repent.