The Apostle Paul gives us insight into this story in Galatians 4. When speaking about the persecution those who had received Christ received from those who insisted on being orthodox Jews he says:

Galatians 4:29 But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now.

Ishmael persecuted Isaac, he looked down upon him and laughed at him with scorn. Paul says he did so because he was of the flesh and not the spirit.

What does it mean to be of the flesh? It means that what you can see is all you believe in. It means you are a bottom line person, and before you buy into something you want a cost benefit analysis of what you are giving up and what you are receiving.

For Ishmael the analysis was clear. If Isaac were the blessed son, then Ishmael lost everything. At a time in history when the property was not split up evenly, but the firstborn received everything and then had the responsibility of taking care of his siblings, Ishmael had everything to lose and saw nothing to gain.

Did he know of the promise? Every piece of land Abraham walked would be given to his descendants; every nation of the world would be blessed? He should have known. But those promises were so far off, and losing that inheritance was much more real.

Tim Keller says people cynically reject the gospel not because it promises too little, but because it promises too much. It is too good to be true. It promises another world, where the rightful King is on the throne, where justice reigns and where all are blessed. Because the cynic fears having his heart broken, he chooses to hold on to what he has.

Is your problem with Christianity that it does not seem to deliver very much here and now? Do you perceive it as a civic club, like Rotary where you gain some respect by joining, and take pride that it does something to help the community? Does it give you a sense of self-respect, pride in being an upstanding person?

Let me ask the question negatively, do you see anything more than what Christianity calls you to give up? Does it shock you to find that, yes being a Christian demands a high sexual morality? Yes, Christianity demands absolute integrity with your money, and even insists that you give a percentage of it away? Do you only see the losses?