Whatever started these artifacts was substantial enough. Why is it that they still exist today?
Celtic symbols are very powerful indeed. They originated hundreds of years ago and unlike many fads that society has seen come and go, they still remain strong. Why is that?
I think the place to start is by asking where these symbols originated and for what purpose were they invented. Celtic knots, which make up a significant part of Irish symbols, did not even originate in Ireland. They were created in other areas of Europe then eventually made their way to Ireland. Before Christianity had a real impact on Ireland, these shapes were constructed. To assume that they were designed from a Christian imperative would be false. However, from what I have gathered, I believe that their appearance was due to spirituality and a connection to the divine.
Today we make things like crosses of wreaths for special circumstances that are often times born of a religious philosophy. Many of us are taught about the Bible or books like it that make up a guideline for how we are supposed to show our reverence. Without these materials, we may never know what God was like or what He wanted. Many people today base their beliefs strictly and solely on what these teachings tell them. I am not here to question the validity of these artifacts or beliefs. My mere point is to examine how people knew what to do before having this structured wing.

Before the institution of formal religion, there is no doubt that people wondered about their existence on this planet. Many of them did not have a book to run to or to inspire them. So where did they get their beliefs or values?
It is very likely that people had dreams way back when and an intuition that often could not be explained that lead them to certain conclusions. Although a book like the Bible doesn’t cover what to do if you meet with an angry rattlesnake, your instinct will tell you what to do. Which means that the Druids and eventually the Celts got their information from their instincts. They had a firm belief in the stars and the natural environment around them.
Many of them felt the interconnections of all living things and these were the droplets that led to the ocean of what we now know as Celtic history. It is a rich, complex and multifaceted art-form which in my opinion originated from a great love in all living things and a desire to honor whatever entity had created it all. Either way, that is a foundation that is very hard to dispute seeing that the catalyst was something so intentionally loving.