You must keep the circus going!
Whatever means you use to get people into the church, is precisely what you must use to keep them.
If you get them with a 'religious circus' then you must keep the circus going—you must keep up the entertainment.
If you get them with biblical preaching and teaching, then that will keep them and you will not need the entertainment.
"Preach the Word; be prepared in season and out of season; correct, rebuke and encourage—with great patience and careful instruction. For the time will come when men will not put up with sound doctrine. Instead, to suit their own desires, they will gather around them a great number of teachers to say what their itching ears want to hear." 2 Timothy 4:2-3