'Fail' in the Bible

Now therefore, O Lord, the God of Israel, keep with Your servant David, my father, that which You promised him, saying, ‘You shall not fail to have a man to sit on the throne of Israel, provided your sons are careful to walk in My law as you, [David,] have walked before Me.’

then I will establish your royal throne just as I covenanted with your father David, saying, ‘You will not fail to have a man as ruler in Israel.’