God is not just a word, or just a concept. When (most) people talk about god, they're not doing so in an abstract form.
For instance, when someone says "The car parked the driveway is blocking my exit". They aren't speaking of "car" as some theoretical idea. They're speaking of it as a concrete, real thing, that exists, and has a fundamental impact on it's environment.
"God" to most people falls into this category. It's not just a concept. It's not just a word. God is a supreme being, that exists, and has a fundamental impact on the world.
I think your decision to move from agnosticism to belief, is more your decision to change your understanding of what "god" is... You've re-classified the words meaning.
Every word is just a word. It's kinda tautological, really. Words aren't something that "just exists" — they are invented by humans to communicate, to give names to concepts they share. Some concepts can be perceived as a thing or a property. Like "chair". Pretty much everyone I speak to knows what "chair" is. What they mean by "chair" still varies, but it is more or less similar. The same is true for many "non existent" things, like "blue horse". Because you probably mean by "horse" what I mean by "horse", and you mean by "blue" what I mean by "blue". You could draw it, for that matter.
It is less true and more arguable for more abstract concepts like "true" or "moral". Or "abstract" for that matter. Because it's hard to define them. They are "meta-concepts" so to say. Properties of properties. Meta-things.
It is the least true for "god". Because this concept does not necessarily mean a thing or a property, some people can actually mean by that something that cannot be defined. Of course it can be real, of course it can have fundamental impact on environment, it can be the environment, it can be creator of environment, of both space and time. Or it can be an actual car in the actual driveway, it doesn't really matter. But only extremely ignorant people think that everyone who uses the word "god" means the same thing by "god" as they do. There are hundreds of religions and philosophies, thousands of denominations, millions of opinions. Essentially, it is just people who understand each other using a word understandable to one another, that doesn't (and shouldn't) really make sense to anybody who is of different school of thought. Like "catamorphism" means nothing to a farmer. Except there are much more meanings out there.
In no way it's likely you mean by "god" what I mean by "god". Or somebody else in this thread. Many people are not even sure they know what they mean. Or maybe they mean multiple things depending on whom they speak to. Even within catholic church the understanding of the God varies from "powerful old man sitting on a cloud" to "all of the Universe at all moments of time at once, nothing less, nothing more". And these are only relatively simple meanings — they can be put into words, can be defined, which isn't invariably true.
For instance, when someone says "The car parked the driveway is blocking my exit". They aren't speaking of "car" as some theoretical idea. They're speaking of it as a concrete, real thing, that exists, and has a fundamental impact on it's environment.
"God" to most people falls into this category. It's not just a concept. It's not just a word. God is a supreme being, that exists, and has a fundamental impact on the world.
I think your decision to move from agnosticism to belief, is more your decision to change your understanding of what "god" is... You've re-classified the words meaning.