And here I am!!!
Flags in worship was generated from many texts in the bible, especially the OT where it mentions the use of standards, banners, ensigns, signals - all much the same thing.
Probably the most well known ones are: (NIV)
Exodus 17:15 "And Moses built an alter and named it 'The Lord is my banner' (Jehovah Nissi)
Song of Solomon 2:4 "He has brought me to his banqueting table and his banner over me is love"
Isaiah 11:12 "And the Lord will raise a banner to show the nations that He is gathering together again the scattered people of Israel"
Isaiah 49:22 "This is what the Sovereign Lord says, 'See I will beckon to the Gentiles, I will lift up a banner to the peoples'"
I could go on but there are so many!!
Principly, it is about warfare and putting down the enemy. Get a group of good flaggers in the church (or even just one!) and you can feel things start to move. People's spirits lift and the atmosphere lightens - the enemy has been banished and the Spirit reigns supreme.
For my part, I love to worship my Lord with flags because I believe it is His delight to see the arts used to worship Him, whether it is flags, dance, mime, sketches, whatever. We already use singing, music, tapestries (or banners as wall hangings), paintings, stained glass, sculture, etc., etc. So why not flags?
God led me to use flags and even moved me 260 miles away from where I was to a church where I would have tons of room with a really great worship band and a pastor who has actively encouraged me. I now have a website and a book and still, six years after I started, He is still feeding me with new moves and new inspiration on how to worship Him with flags.
It may not be strictly biblical but it is God inspired. Take my word for it. You can read more in my blog if you're interested!!