Before one can understand the facts about what Paul is credited with writing concerning grafting, one must understand The Seven Noach Commandments and the real purpose for the destruction of the world by flood. In brief, when Hashem created the world He established it with natural laws and spiritual laws which are still in effect. One of the natural laws is like being with like and kind being with kind. Unfortunately mankind has broken the laws of nature many times. Man has experimented with seed mixtures of animals and plants for hundreds of years.
Most humans think little of it.
Mankind does not think of such experiments as altering Creation as G-d intended it to be. Mankind does not consider that improper mixtures of seed was one of the primary reasons the first world was destroyed by water. Unfortunately most of mankind accept this lack of restraint as normal. That being the situation it is pathetically understandable when we as Jews read or hear such outlandish claims as Paul taught about grafting. This is one of the Seven Noaic Commandments given to every human which is still in effect today.