Religion builds on traditions built up over thousands of years. Nobody ever really throws it all out and starts over. The gospel writers did what they considered to be their civic duty as Jews to explain and embellish the story of Jesus to fit earlier Jewish myths, as a lure to get them to investigate the new ideas that He brought to the world.
From our perspective, there was no need to claim that Jesus was a direct descendent of the line of David, but to the ancient peoples of Israel, established theology is extremely important. Religion had to make sense, it wouldn’t be for thousands more years before humanity could figure out how to make the world make sense without these sorts of tricks.
Ancient Hebrew myth told of giant monsters that roamed the Earth and filled roles that God needed doing. And of divine beings, called Elohim, which, like the Norse deities, had outsized personalities and fought with each other and possessed no morality like humans did. They were the agents of a capricious world, beings with the power that we could only wish we had; stories like that of Job dealt with the horrific mental states created by that caprice. The Old Testament was the cultural output of a society desperate to make sense of a senseless world.
Religion explains some things, and leaves other things unexplained, expecting you to fill in the gaps yourself. Let us take the foundational creative myth underpinning Abrahamic cosmology, that of Adam and Eve. Have you ever stopped to think how utterly short the story is? It’s not an accident. Even shorter is the story of Cain and Abel. It’s not explained, for instance, precisely what it was about Cain’s offering that God spurned.
Part of this is the stories are cultural. Just like a movie, there just isn’t much room for explication. Another part of it is to facilitate what we in the computer industry call user interaction. You want people to use and interact with theology and allow it to inform their lives. This is best accomplished when people can make up their own answers to things that aren’t super-important to the orthodoxy.
One unanswered question of Christian soteriology is whether there’s an intermediate area between Heaven and Hell for people that aren’t good or bad enough for either. But you might be surprised to find that Hell, the whole concept, isn’t specified directly in the Bible, it’s just inferred by later Christians as a necessary consequence of the idea of Heaven along with a few of the gospel stories depicting the afterlife.
In fact, the entire conception of the afterlife that Jesus had was very different than both the predominant conception that Jewish society of the day had, and the insufferably moral conception that later Christians developed, where you could imagine a big scorecard in the sky whose contents determined a life of absolute bliss or misery. Jews never had much use or interest in a world outside of the physical one, and their conception of morality was so constrained by laws and divine commands that they never bothered fleshing out what happened immediately after death. Jews were chosen, God wants them to rule the world. This world, not some imaginary Heavenly realm that’s just so eye-rollingly convenient.
Christian soteriology had to deal with the fact that the God that they were looking towards didn’t choose them, you had to choose God, or else. Jesus was a Jew, Jews had no reason to actually fear God, this is why throughout recorded Jewish history, Jews fearlessly walked away from God knowing that God wouldn’t ever fully abandon them, see the book of Jonah for a hilarious explication on that idea. Jesus’ cosmology rested on his understanding of himself as a Jew. Only someone whose self-conception included an unbreakable covenant could have believed his inner voice telling him he was the son of God.
All that Hell nonsense came later, as Christians grappled with inducting people into the faith who had no preexisting covenant relationship with the Lord. A covenant wasn’t just some random deal, it was a specified series of demands and institutionalized interactions with the deity that had the force of law, and custom and literature helped you understand that relationship.
All this is to say, is that if it’s important enough to specify, religious authorities will do that. But they’ll never specify so much that you won’t have questions to ask and seek answers for. Seeking the answer to existential questions is the quintessential spiritual activity, precisely the thing religious authorities want to see.
So you can have your own religion intertwining interestingly and usefully with the established tradition. A spirituality you can call your own, one that will mix it up with everybody else’s spirituality and create the zeitgeist for the next big movement.