One of the best statements about pastoral ministry I've heard or read came from H. B. London, Jr. He wrote that if you are serving in a good, strong church it's because someone stayed there and made the church that way. If you are serving in a church that is not so good or strong, perhaps God is calling you "for such a time as this." He has you there that you might build it into a better church. I believe there is much wisdom in those words.
I served my first church for 20 years before accepting a call to our Region staff. Before I went to the church, the average pastoral tenure over several years was 12 months. That was the average! The church was not healthy when I went there. I was told later than the church had considered closing but decided to try one more pastor. Perhaps if I had known that before I went I would have reconsidered going there, but I'm glad I didn't because those 20 years were some of the best years of my life.
Virtually every study done on strong churches find that they have had long-term pastoral leadership. The pastor had planted roots in the church and community. People came to trust his leadership. He or she had built relationships with members of the congregation. The pastor and congregation truly loved one another, shared a common vision and worked together to fulfill that vision.
This does not happen in churches with revolving-door pastorates. When a church has pastors who leave every 2-3 years they begin to wonder what's wrong with them. A low self-esteem can begin which limits what the church believes it can do. It doesn't take long before a new pastor picks up on that belief causing him or her to begin searching for another church. Nothing changes until a pastor decides to stay and move the church out of the negative rut they are in. It will be a slow process, and many pastors will decide it's not worth the trouble. But, those who stay and begin to rebuild the church will find that all the trouble and pain was well worth it.
Some pastors will retire after a 40 year ministry, but when they look back they will find they didn't have a 40 year ministry; they had 10 four year ministries and never really accomplished very much. How much better it might be if they had invested those 40 years in just one or two churches.