Mark 13:20

‘And unless the Lord had shortened the days no flesh would have been saved. But for the elect's sake, whom he chose, he shortened the days.”

The destruction and killing would be so bad that if the Lord did not intervene none would remain alive. But we are told that He would shorten the days ‘for His elect's sake'. Even though many of the Jerusalem church had fled there would still be in Jerusalem those given by the Father to Jesus, and the idea is that many of them would be preserved, and others would therefore be spared with them. We can compare how God marked off His own in Ezekiel 9 at a time when the previous city and Temple were to be destroyed. The thought may even be that God stayed the hand of Rome to some extent so that some would survive and become Christians as a result, having awoken spiritually during the siege. Thus would good come from this final destruction. The parallel with Mark 13:13 suggests that we are to see in this more than just physical survival. ‘When God's judgments are in the earth, the inhabitants of the earth learn righteousness' (Isaiah 26:9). It must, however, also include physical survival.

The idea of ‘the elect' is prominent in this passage (Mark 13:20; Mark 13:22; Mark 13:27). It does not occur elsewhere in Mark. But here they are those whom He chose, and it therefore clearly refers to those who have been ‘given to Him' by His Father (John 6:37; John 6:39; John 6:44). They are those who behold the Son and believe on Him (John 6:40). They are His new nation (Matthew 21:43), His new ‘congregation' (Matthew 16:18), living branches of the true Vine (John 15:1). For the idea of God ‘shortening the days' of His judgment compare 2 Samuel 24:16, where He stays the hand of the avenging angel; Isaiah 65:8 where He declares that He will not destroy all for His servants' sake.