What have I got myself into?

Long story short: Bear broke into my shed. Wrecked door. I replaced
door. Basic sheet of 3/4" plywood, bordered by 1x4's (?,
1-3/8"X3/4"). I did not paint them.

Now, couple yrs later, I'm getting a lotta 'splinters' from the 1X4's.
Should I paint?, sand?, replace wood?, all the above? I'm not real
experienced, but willing to learn.

nb