The devil will try to upset you by accusing you of being unworthy of the blessings that you have received. Simply remain cheerful and do your best to ignore the devil's nagging. If need be even laugh at the absurdity of the situation. Satan, the epitome of sin itself, accuses you of unworthiness! When the devil reminds you of your past, remind him of his future!
– St. Teresa of Avila
Perhaps thanking God for the blessings he gives us is better than worrying over whether or not we are worthy, because God is a generous and merciful God.