How do we know that God's people are always His people?

The sermon points out that once God has a people, they remain His people eternally. This is rooted in the assurance that God does not change—He is the same yesterday, today, and forever (Hebrews 13:8). The phrase 'My people' signifies that their identity as God's people does not alter even when they stray or become lost. The history of God's people shows this consistency, as seen from Adam through the New Testament believers. They may be lost at times, but they are not lost to God, who recognizes them as His sheep.