Typically membership means meeting some kind of a standard - you have to be talented enough for the athletic team or drama team or smart enough for the debate team or rich enough for the country club. Membership can sound dangerously exclusive and isn’t Christianity about free grace - so how can we set up standards without becoming legalistic or moralistic? This is one of the key reasons - people resist the church - and maybe one of the key explanations for much of the hurt associated with churches.
Jesus Kingdom is inclusive but in a way that's counter intuitive and counter culture. It’s not a person’s moral perfection that qualifies them as a Christian and membership in the church. It’s the opposite. It’s their recognition of a lack of moral perfection coupled with a hunger for it. It’s not the people who never sin; it’s the people who wrestle against sin. A local church’s ministry is to affirm - not the righteous but the unrighteous who thirst for righteousness—the righteousness that Jesus gives.