The train of His robe has to do with His glory and beauty (Exodus 28:31-34, Exodus 28:1-2)
But unlike Israel, there is no uncleanness in the train of His robe (Lamentations 1:9)

The train of His robe had to do with His omnipresence (Isaiah 6:1-3)
There is nowhere you can go to escape standing on the train of his robe (Psalm 139:7-16)

The train of His robe has to do with caution (Isaiah 6:1-5)
The Seraphim are very cautious as they are on the train of His robe (Isaiah 6:2-3)
Isaiah is very cautious as He is on the train of His robe (Isaiah 6:5)

*But this Majestic Holy One of Israel, laid aside His heavenly privileges, came to earth and lived retaining His spotless robe, and was made to be sin, so that His spotless robe could become ours (2 Corinthians 5:21)