I have seen the light.

 Slowly take the stile off the tenons. When you can see the light, you know you're winning!

Gentle taps and leverage; these mortices possibly haven't seen the light of day for 400 years.

What a joy to see the evidence of the original joiner working the wood. The runout of the plough plane through the tenons, shavings made when chopping out the mortices still in the bottom of the mortice! If you've been careful ,the holes in the tenon should be intact enough, to pull the joint together again.

Place the half of the pulpit to one side and set about removing the broken panel.