One of the challenges for ministers when we leave a church is to actually leave. Too many of us want to return to conduct weddings and funerals. It's even more difficult when the minister resides in the same community as the church he or she is located. I've known church members go to the former pastor in such situations to discuss things with which they disagree in the church. Unfortunately, I've also known pastors who would then interfere in the affairs of their former church. Of course, they did so with only the most noble of reasons!
The denomination in which I serve asks our ministers to sign an Ethics Statement. No minister is required to sign this statement, but many of us do. One of the items on the statement addresses the issue of how a pastor should relate to a church he or she has left. Unless the new pastor requests that we participate in an event we should stay away. I realize it's not easy, especially when it involves people with whom we had a strong relationship, but it's the only way the new pastor actually will be able to become the pastor.
I was thinking about this recently when our current president stated that he would actively work to protect his legacy. The vast majority of former presidents have stepped out of the picture when the president-elect was sworn in to give him space to form his presidency. 43 remained virtually invisible after leaving office even when his legacy was under constant attack by President Obama and his advisers. He was merely following the example of those who had preceded him.
Some pastors give the same reason for remaining involved in the church they've left. They feel that their legacy is so impressive or so important that they have to protect it even if it means interfering with their successor. Frankly, in my opinion, a true legacy should not need protecting. It should be so important to the organization that it will stand on its own until it is no longer relevant.
I agree that it can be hard to watch things we've built begin to fall apart when we leave. I had to watch that happen in a church in which I served for 20 years, and it's not easy to not step in and try to protect the work you've done for all those years. However, this is the ethical thing to do regardless of whether the person is a pastor or the president.
To be called to another church and try to interfere with the previous church is a sign of either arrogance, immaturity, or both. It's also a sign that we can not trust God to do what is best and therefore we have to help Him out.
When you leave a church, leave. It's OK to remain friends with people in your former church as long as you set strict boundaries that ensures you will not interfere in the life of that church. It's OK to return to help in a wedding or a funeral IF the new pastor personally calls and asks you to participate. It's certainly fine to keep your former churches in your prayers, and it's very important to praise your successor whenever you have the opportunity.