How do you know if a church is just there to entertain?


It caters to what people want. The Bible is rarely if ever referenced. Few people ever ask if this is according to what God authorized. You hear people talking a lot about what they feel should be done and no appeal to what God said. What attracts the most people is what is most desired.
"I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel, which is not another; but there are some who trouble you and want to pervert the gospel of Christ. But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed. As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed. For do I now persuade men, or God? Or do I seek to please men? For if I still pleased men, I would not be a bondservant of Christ" (Galatians 1:6-10).