Gas oven wont light up

For the last several weeks, the oven has been slow to light. Now it wont light up any more. The Igniter is cherry red and seems to be working but the gas valve doesn’t open so the oven wont light up. The broiler is working fine as well as the stove top.

What can I check and how, to determine what’s wrong and figure what part to change and how?

Please help.