This letter is my personal notice to you that I will be resigning as leader of (church). With your blessing, my last day will be (date).
I have prayed over this decision for quite some time, and the Lord made it known to me that it is time to move on. My entire family will miss our (XX-year) church home dearly, and will continue to pray for the congregation to grow in accordance with God's plan.
I would consider it my honor and pleasure to assist the congregation in any way as you search for a new (pastor/reverend/etc.). I can be reached at 555-555-5555.