Approximately 13,700,000,000 years ago, the first thing to happen, happened. According to the best current astrophysical theory, energy of an infinite quantity was emitted from a point of no dimensions. Since that point had no dimensions, it did not occupy space, and indeed, there was no space before that, and even more startlingly, there was no “before” before that, i.e., no time, no space. Thus there was no thing in that “now”, “present”.
For any person to be able to “conceive” of a such a state, that person would have had to have had a sensible experience of that reality prior to his/her being able to conceive of it. Thus, for a person to conceive of a “whale”, that person must have had a previous sensory experience of a whale, either in the flesh or through viewing a photo or sketch of one. A person can also construct a concept by having experienced an object in parts, i.e., one can conceive of a “flying green whale” only because one has had a previous experience of “whaleness”, “flight”, and “greenness”.
Thus, God, if there is a God, must be humanly inconceivable, unless the “conception” was by God Him / Her self. This is what Christians believe; That God whom we cannot conceive, conceived of Himself in the womb of a young Jewish girl with her permission, and took on all the limitations of humanness. And when we ask “Why should we believe it”, one can only come to the conclusion that someone absolutely trustworthy has told us to believe it, and since we absolutely trust that person, we can say “I believe you.”
But what person do we hold to be absolutely trustworthy? We might say, “Our mother”. I certainly would hope so, but some mothers are not trustworthy. Some may believe, but in light of events in their lives, they may entertain doubts. So whom would we trust then? Well after reading all about Jesus, his life, his teachings and the way he died, we might reasonably say, “Jesus”.
And that is what Jesus apparently asks of us according to the accounts in the NT wherein he comes into Galilee as an unknown adult and says: “ The present moment is the right time, change the way you think about reality, for the Kingdom of God is WITHIN you. Believe this good news.” [Mark 1:14-16]