'Adding' in the Bible

Therefore, lo, I am adding to do wonderfully with this people, A wonder, and a marvel, And perished hath the wisdom of its wise ones, And the understanding of its intelligent ones hideth itself.'

Go, and thou hast said to Hezekiah, Thus said Jehovah, God of David thy father, 'I have heard thy prayer, I have seen thy tear, lo, I am adding to thy days fifteen years,