A lukewarm Christian is someone who claims to be a believer in Jesus but does not appear to be committed to Christ, may occasionally attend church, rarely reads the Bible, and dabbles in the sinful things of the world. Such so-called Christians appear to be Christians in name only but are most probably false converts.
Romans
Chapter 12; 1 I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.

2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.