"I will strike her children dead. Then all the churches will know that I am he who searches hearts and minds, and I will repay each of you according to your deeds. Now I say to the rest of you in Thyatira, to you who do not hold to her teaching and have not learned Satan's so-called deep secrets I will not impose any other burden on you. Only hold on to what you have until I come." (Revelation 2.23-25)
Satan's deep secrets in Thyatira were either false teachings advocated by heretics, or secret insights by so-called believers which were guaranteed to promote deeper spiritual life. It is a warning that we should hold tightly to the basics of our Christian faith and view with caution any new teaching that turns us away from the Bible, the fellowship of our church, or our confession of faith.
The so-called "deep secrets of Satan" are literally, "the deep things of Satan" which may be a scathing reference to the perverse teaching of the Nicolaitans Sect also called Nicholaism. We cannot hide from Christ for he searches both our hearts and our minds, and still he loves us. The sins we try to hide from God need to be confessed to him. "Her children" are those led astray into pagan immorality and worship. Their punishment is absolute.
In this Revelation passage, "Searches hearts and minds" is translated in the Authorized Version as "searches reigns and hearts." "Reigns" are literally kidneys, which were regarded by the ancients as the seat of the emotions. Every emotion and thought is open to God's gaze. No one will deceive the Risen Christ. "Satan's deep secrets" are known to the God "who searches our whole being." God knows us, our thoughts, feelings and intentions. Our God searches the innermost thoughts of our minds and the most tender feelings of our hearts.