How was your year?
"It was really intense. We had to grow in our faith a lot. I'm not sure anyone could be completely prepared for this kind of experience, but Diety brought us through it. I have hope our work made a real difference." (mix and match)
if it someone you are close with, you could add, "I sure am glad we had friends like you to lean on!"
Thank you for serving/sacrificing:
"It is important work. Thank YOU for being a friend/ for your support"or
"Oh, it's not about us. It's about (object of the work)", or if religiously appropriate,
"Oh, don't thank us, thank Diety for making the (object of the work) possible"