Ancient Israel looked forward to the day of the Lord, that day when everything would be set right. Enemies would be scattered, the sick would be healed, the poor would know comfort, and all people would experience peace. Even though Israel had suffered terribly, God had made promises to their ancestors, and God always keeps promises. Initially, they expected that day to be one of punishment and retribution for their enemies, while they would enjoy vindication and blessing. Today's first reading asserts that Israel will enjoy no preference. If they sin, they also will face the righteous anger of God.
In the Gospel passage, Jesus describes the terrifying events that will precede the destruction of the temple. This was probably less a prophecy of a future event than it was a warning of the suffering they might have to endure as his followers. Such suffering would pave the way for the fearful day of the Lord. If they persevere, such affliction would be purifying for them rather than punishing. Though the reading does not include mention of the day of the Lord, it would have been in the minds of those who heard Jesus' words. Many would believe that God's ancient promises were about to be fulfilled.