Nothing in this life is permanent. And so we prepare.
Luke 21 is about when everything fails.
1. False security. (v5,6) Psalm 48 refers to the beauty of Jerusalem and the temple. The disciples assumed that the end of the temple would be the end of the world (v7-9). 'The end will not come right away'.
2. Where is real security? (v12-19). The trouble will come to those who follow Jesus (like as told in the book of Acts.) Jesus' Name - though Him we gain life. One greater than the temple had come. Israel relied on what God had given them, and not on God Himself. A trap we can fall into. Is our security in God Himself?
3. Don't ask Jesus for a sign (Luke 11:29). (v7). Sign watchers are vulnerable. Note the word 'desolation' (v20) Like the prophets the warnings if they don't obey (v22). They are planning to kill God's Son, and so destruction will come. (v25-27) - could be a description of the end of the world, but more likely to refer to His death and resurrection. (v28,31) - God's redemption is being accomplished in the death of Christ. Redemption is now near to all who put their trust in Him.
4. What to watch for. Not signs, but rather themselves (v34-36). The way to be ready is to put our trust and allegiance in Christ. Looking for signs can distract us from doing what we should be doing now. We are ready for the end, whenever that may be.
