Why is the train filled the temple significant?

The phrase 'His train filled the temple' in Isaiah 6:1 signifies the abundant glory and majesty of God as He reveals Himself. It provides a picture of God's perfection and the completeness of His character. The imagery of the train, reminiscent of the high priest's garments, suggests a profound connection to His sacrificial role and His representation of the believers before God. Just as the high priest wore a breastplate bearing the names of Israel, this imagery implies that God's people are encompassed by His sovereign grace and mercy, assuring them of His continual presence and guidance.