If anyone doubts that he has been personally forgiven, he accuses God of lying:
... consciences cannot be made tranquil, unless they know that it is God's command and the very Gospel that they should be firmly confident that for Christ's sake sins are remitted freely, and that they should not doubt that these are remitted to them. If any one doubts, he charges, as 1 John 5, 10 says, the divine promise with falsehood... Therefore, if any one be not confident that he is forgiven, he denies that God has sworn what is true, than which a more horrible blasphemy cannot be imagined.
(Apology of the Augsburg Confession, Article XII, paragraphs 88, 94)