Increasingly, I’ve come to be convinced that one of the chief reasons many people stay with a congregation is habit. Human beings really are creatures of habit. This is why weekly services, and annual holidays, are so important:— If you are in the habit of attending a weekly service, you will be more likely to stay with a congregation in spite of dissatisfaction and annoyance. If you are in the habit of attending an annual holiday observance (e.g., Christmas eve candlelight service, etc.), you will likely attend year after year in spite of the quality of the service or theology of the congregation.
This implies that anything that might cause people to break their habits will lead to some people drifting away from a congregation. If you have no Sunday services during the summer, at least a few people will get out of the habit of showing up, and they will drift away from the congregation. If you have two worship services during most of the year, but only one during the summer, you will lose at least a few people over the summer (I watched that happen at the Palo Alto church over the past summer — we lost at least a couple of newcomers). If your minister disappears for two months during the summer, and instead you have guest preachers or lay leaders, I would be willing to bet that at least a few people will drift away from your congregation, for you have broken their habit.
It seems to me that if we are looking for ways to get newcomers to stick with our congregations, one of the main things to do is not to get people to think about theology, but rather it’s to get people to develop the habit of congregational life.