I'd also note that "ultimate reality" is different than "truth" or "reality." Merriam-Webster itself clarifies this: "the supreme or ultimate reality, such as the Being perfect in power, wisdom, and goodness who is worshipped as creator and ruler of the universe."
If you look at the instructions on how to use the dictionary, that part after the "such as" is subsumed, not exhaustive.
Certainly The Ultimate Reality is seen as these things and worshipped as creator and ruler of the universe. However, the integral part of the definition is "The Supreme or Ultimate Reality", and this conception of the monotheistic God is universal, even in cultures alien to the Abrahamic faiths.
But something that needs to be understood about Christianity is that it very much looks like the opposite of what it really is sometimes, and it is something that goes to the very founding of it.
But as even St Augustine once wrote, True Religion has always existed, since the beginning, and in his day it took the form of Christianity.
The Ultimate Reality is God. That is the foundation of True Religion. Everything else is abiding in that. It's easy to get confused by cultural things and the power plays of politicians and wizards. Christianity teaches that God is King and Savior and we are really all in this together. The Church is Catholic, or Universal. Just because an institution claims to be universal does not make it so. The Church is the body of Christ, of whom all things were created by, exist in, are sustained, by, and have eternal life through.
It's a mystery, but that doesn't mean that it is meaningless, and even mysteries can be understood. But they can't be understood if you don't believe. The very foundation of faith is that God exists. If you don't believe this, you can get nowhere. This is a dead tree, and self condemnation.
If it wasn't so, things wouldn't be the way they are, and God made things the way they are. It's really quite alright.
But Christianity is about being a disciple of God. If God is The Truth, there is clearly a right way and a wrong way to love God. After all, we are loving The Truth, which is incompatible with loving the things of this world. To love God more than the things that satisfy the lusts of the senses and mind is very alien to a hedonistic culture. Christian theology sees this as idolatry. These things bribe usnaway from The Truth. And they clearly do, at least to those with eyes to see.
So Christianity is very very misunderstood because most people are superstitious. Believers and unbelievers.
But what is it really all about, cutting through it all?
The Ultimate Reality is God. Love God with everything. Show others charity, because you have been wrong and are still wrong. If you hate someone for being wrong, you condemn yourself because you aren't any better. Forgive.
But if you get nothing else, get that The Ultimate Reality is God, because that is what this topic is about.