The Heraldry of Wales
Despite its occasional use by other figures famous in Welsh history, the red dragon became the symbol of the Welsh nation through its adoption by the Tudor ancestors of king Henry VII. Edmund and Jasper Tudor had a dragon as crest and supporter to the arms granted them by Henry VI. When Henry Tudor faced king Richard III at the battle of Bosworth in 1485 his battle standards numbered three. One of these carried the arms of St. George of England, one the arms of the house of Beaufort and on one was a “Red ffyry dragon peyntid upon white and Grene Sarcenet”. It is held that this dragon banner represented Henry Tudor’s claim to be a true representative of the ancient kings of Britain and served as his tribute to the Welsh people who had made his victory possible.
The above is from http://www.data-wales.co.uk/flag.htm and shows when the flag of Wales reemerged. King Henry VII used it to claim his right as part of the ancient traditions. Part of the ancient traditions would have included the ancient traditions of faith. This was part of the rise of the Tudors and its next in line was the infamous Henry VIII. The War of the Roses likewise results in the Tudor Rose. The order of the colors in the Tudor Rose matters. During this same period the Rose becomes the symbol of the Lutherans, though perhaps with inverted colors, when the prince elector who backed Luther gave it to him to use. Shortly thereafter it emerged also as the symbol of the Rosicrucians.