If the oven ignitor gets hot (glows) but oven will not light then it is likely that the igntior itself is faulty. Or it lights but does not get hot enough so it goes out.
The ignitor has a very specific resitance that allows a critical voltage to be supplied from the ignitor to the gas valve. If the ignitor has so much as a hairline crack, the resistance of the ignitor will increase which in turn will decrease the voltage to the gas valve. As a safety feature, this will result in the gas valve not being able to open and no ignition will take place. The recourse in this case is to replace the ignitor.