This passage in Revelation links back to the Old Testament. A strong case can be made that that in the end times, Israel, after a long period of rejecting the Messiah, will be restored. At that time there will still be hard-hearted doubters, but just the same, God gives us as believers a hardness/strength in our belief. We are to be faithful and preach God's Word giving no thought to rejection, leaving the outcome to Him!