One Heart was curious about the meaning of the Celtic knots in this commission piece, so I did a little research and discovered this...
It's not clear that Celtic knot drawings were ever meant to sybolize anything, but lots of modern people think they contain spiritual concepts. The knots are incredibly popular with followers of new age religions, magic societies and all sorts of other groups who want to draw an association with the oldest traditions of Ireland. They also look pretty cool on T shirts.
Some historians think the Celts drew these symbols because they were prohibited from drawing any other pictures. One of the more widely accepted theories to explain the Celtic knot meanings says that Celtic religion, like Islam, may have prohibited realistic depictions of living creatures. This rule may have given birth to the complex Irish knots.
The small knots at either end of my commission piece are a "Triskele" or Triangular design. The larger center knot is one of the Circular designs. Some view these as symbols of cycles of life or eternity, but they are also seen as a sign of unity. The "endless" quality of Celtic knots seems to make lots of people assume they symbolize time without end.
We'll never know if these meanings were there for the Celts. A key reason the knots are associated with religion is that after the Christians came to power in Ireland, they adopted the knots to their own religious purposes. And to further complicate the issue, many scholars believe the knots may not actually come from Ireland, but were simply brought into Ireland when Norsemen conquered the Celts. Designs that seem similar to the Irish knots have been found in old Italian and British manuscripts, and on pottery and architecture in other parts of Europe.
The best historical explanation may be that from the sixth to the eight centuries a long series of wars took place between British, Irish, Scottish, and Scandanavian tribes, which meant that both winning and losing groups of warriors wound up living in each others countries for considerable periods. The Influence of all these cultures on each other may be what really gave birth to a style now called Celtic Interlace.
I found that to be very interesting! Thanks to One Heart I'm a bit more knowledgeable...