The hardening work of God isn’t an easy subject to broach initially, but Justin Taylor provides sound guidance on it.
Before you answer that question, make sure you read Denny Burk’s thoughts on the matter. He argues that Paul was, indeed, married and then widowed.
Bill Mounce also weighs in on the question and concludes differently.
UPDATE: Burk returns to the subject in order to add further support for his position.