Atheists love to ask how Christians decide that “it's your God instead of some other religions's God?”
Well, when one gives just a few moments of thought about what would be required to bring a material, mathematically precise, life sustaining, moral universe into being out of literally nothing material, it doesn't take long to rule out Thor and Krishna and what have you. It doesn't take long to realize that you can have only one Greatest Conceivable Being.
However there are a lot of people in the world that, like atheists, reject Creator God in favour of an impersonal moral authority called Karma. And, true to form, in the West, the arrogant West, we take Karma, twist it and bent it and shape into a form that forces Karma into something by which we're always getting better and better. That's because, like atheists believe, “We're really good people.”
Karma on the other hand is found in a reality whereby simply not picking up a banana peel is enough to make one regress in form / being. Karma, in “reality” creates “An endless wheel of rebirth and suffering.”
So why can Christians can reject Karma?
If a Creator God is rejected, then observation could make a person think that along with mathematical laws, laws of logic and laws of objective morality, one could posit impersonal moral laws that seem to reside in us. This is what atheists and reincarnationists propose, though for different reasons. If you think about it however, you would see that these moral laws must be quite complex indeed. So complex that these laws are able to regulate the connection between the soul of every single person's moral life now, today, and the same soul's total and complete circumstances in the next life. This would include the power to dictate what kind of body the soul will have, where it will live and how much pleasure or difficulty it will experience.
This, or perhaps these impersonal moral laws would have to be able to take into account every single act, every single intention (see Bhagavad Gita and the banana peel) and every single choice that has been made for every soul that's ever existed and make certain that person gets nothing less than exact and perfect justice in the next life for actions performed or not performed in this life.
So what's the problem with this? Why would a Christian reject this type of absurd belief system in favour of that which was taught by Jesus? Well, the degree of complexity required by these moral laws is beyond imagination for something immaterial, inanimate and impersonal. Especially when Karma's goal is to achieve perfect justice. But we know that brute facts do not possess the ability to bring about justice. Brute facts just are. “Two plus two equals four,” doesn't DO anything.
On the other hand a structure that promotes justice seems intuitively probable. A moral order that we all believe exists calls for an Intelligent Agent along the lines of something that Christianity describes. This Intelligent Moral Agent, from which objective moral values, duties and obligations emerge is far beyond anything a human agency could produce. It requires an appeal to Divine Intelligence. That is why both atheism and reincarnation type beliefs point directly to a personal God.