I'm not sure I'd care to pass through half a heifer even if the birth of the promised heir depended on it. The Bible contains a lot of material that I find odd or even offensive and when I read stories like this I can’t imagine God needs to be so dramatic just to make a promise come true. So if we were to demythologize this story, or take out the bits that don’t fit our view of what is real and what might not be quite the way it reads, what would be the harm? Maybe it is because we need the bits “beyond our knowing” so that we can live more fully the part of this story that is real to us - when we like Abraham find ourselves between what is and what we hope will be. If we have worked out all the details, made God fit our way of thinking, what do we do when we don’t fit God’s way of being? Abraham’s faith reckoned to him as righteousness, or right relationship with God, depends on believing the promise when the promise is not yet. It means trusting God is present when all evidence would indicate that God is not. Faith lives between what is and what is hoped for, between the revealed Word and the mystery of the Word invisible yet somehow present. So Abraham believed what he knew could not be and we are the offspring he was promised, counted among the stars he could not number.