The popular thing to write on one's 50th anniversary is a glowing tribute to one's spouse in admiration for her patience and perseverance, but I know also that few would benefit from reading that. What interests people and benefits other marriages is learning from our mistakes.
As disciples, we are called to grow and multiply; the good news is given to us like the talents were given to those servants in Jesus’s parable (Matt. 25:14–30). Consider: Every time you hear the Word of God preached in your local church you are given a coin, a talent, which God calls you to multiply according to your ability. We are responsible and accountable to God for what he has given us.