As pastors, few things hurt more than seeing people show up to our churches, then leaving as quickly as they came. Some leave without reason. We had this problem at The Journey Church, where I pastor, for many years. We constantly had new faces at church. Folks enjoyed the worship gatherings and talked about how friendly people were, but after a short time they were gone.
As a church who desires to reach people and make a difference, seeing new people not stick hurt. Our backdoor was massive. Plugging the drain was a big issue.
As a staff, we were tired of the revolving door. We were working too hard to reach people only to lose them. So we worked to pinpoint the reasons we were were losing people. We discovered three dominant reasons. These three things are now on our radar. We constantly think about systems, communication, structure, and strategy for fixing these three issues. Here they are:

1. Unknown – They feel disconnected

If people come to your church and still feel like an outsider after a couple of months, they will leave. People desire to be known. People want to be connected. Good worship services and strong preaching are great for attracting people to the church, but they are not enough for keeping people in the church. You must have a plan for assimilating people into community. Folks attending your church need to eventually hear some people call them by name.
At my church, we have a Next Steps/Meet-The-Pastor each week, after each service. This lasts less than 10 minutes. I share the church’s vision. I tell them how much we need them and how excited we are they came. We tell them their next step is either to serve in a ministry and/or  find a Gospel Community (group). During the week, we send an email, thanking them for coming, and remind them of their next steps.
Questions for assessment: Do we have a lot of people coming on Sundays who are unknown and anonymous? What are we doing to move people from showing up to becoming known?

2. Unneeded – They feel unwanted or not needed

People want to make a difference. Nobody likes to be the last person picked before the kickball game. The Church’s mission is big and laborers are needed for the harvest. We should be constantly encouraging new people to plug into the mission and serve on a ministry team. At our church, we were terrible about getting people to serve. We had needs, but we failed to make them clear and to boldly ask people to help. When people believe the ministry needs in your church are “taken care of” or full, they will leave.
At my church, we have a Connection Point we direct everyone to. We communicate constantly that a next step is to serve and find a ministry. There we have all the information about areas to serve. When they sign up they get a call from the staff member with oversight of that ministry and move into service.
Questions for assessment: Do people genuinely believe there is a place/need for them in our church? What process/system are we deploying to get people serving in an area of need and giftedness/passion?

3. Unmoved – They feel stagnant or not growing

People need to be growing spiritually. It is great for them to meet people. It is wonderful for them to volunteer and serve. But if people are not maturing as Christians and growing closer to God, you can lose them. People are prone to ruts. Drifting into ditches is our natural gravitation due to our hearts being out of alignment. Our faith must be cultivated daily or it wanes. As pastors and leaders, that means we cannot assume people are growing.
At my church, we ask these questions: How does the unbeliever learn the gospel at TJC? How does the new believer learn the basics? What resources or opportunities are we providing to mature and deepen believers?
Questions for assessment: In what way are we ensuring people are truly growing spiritually? How do people get discipled at our church?
There could be other reasons why people leave your church. Conflicts between families can arise. People can disagree with decisions made. People find other ministries that match up better for them. People move. There are many reasons people can leave, but the three things I outlined you are responsible for. These are three things you must have systems, strategies, and plans to monitor.
Idea for Implementation: Meet with your staff, deacons, elders, or leadership team to go over these three things and answer the questions for assessment together for your church.