Abraham built the Kaaba with the black stone and used it to worship Allah. According to the bible this makes Abraham a pagan.
It also makes Abraham a demigod because he made the Kaaba holy because his feet and bodily contact made this ground holy. This is something that only a demigod and not a mere mortal is capable of accomplishing.
Mohammed killed to take control of the place that his demigod Abraham had earlier made sacred by bodily contact and worship.
These are just some of the reasons that biblical Christians reject Islam.