If you're tempted to doubt the grace of God, then hear this reminder from Luther:
Although sin does still remain in our flesh, and we daily fall and offend, yet grace is more abundant and stronger than sin. The mercy and truth of the Lord reigns over us forever. Wherefore sin cannot terrify us, nor make us doubtful of the grace of God, which is in us. So long as Christ, the vanquisher of sin, is at the right hand of God, making intercession for us, we cannot doubt of the grace and favor of God towards us.
--Martin Luther,
Commentary on Galatians