Saying you’re a part of the Church (universal) without being a member of a specific local church is like saying you’re in the NFL without actually being on the roster of any of the NFL’s teams.
The NFL is made up of its 32 teams. The Church — the universal body of believers from across space and time — is manifested through the multitude of concrete, local churches.
Some may point to exceptions: “But what about…?” “But if you say this, doesn’t that mean…?” But there’s a reason these are exceptions — they are exceptional; they are not the norm.
The Bible both states and assumes that those who are identified with Christ by trusting in him are also those who are identified with him in baptism and identified with his community of believers — the church — through inclusion/membership among their ranks.
To abstain from regularly assembling with and committing oneself to a church community, placing oneself under its leadership and discipline, is to break away from the Biblical pattern of the Christian life — a life lived out in community, with mutual-accountability and encouragement.
To speak of “regular attenders” as some secondary class of pseudo-members is to blur these lines. We are better off to speak of such folks in truer terms, of what they are — perpetual visitors.