The Apostle Paul is citing the prophet Isaiah’s prediction in Isaiah 10:22 of God’s judgement upon Israel by the Babylonians because her sins. However, God will preserve for Himself a faithful remnant though Israel was a great multitude. By quoting this text, he is calling attention to the parallel that among the Jews of Jesus’ day, many rejected Him but there is a remnant who received Him. Truly, Jerusalem was destroyed by the Roman army and the Jews scattered in A.D. 70.