Chapters 9-11 in Romans deal with Israel’s relationship to the church. Shockingly, Paul says that not all of the physical descendants of Abraham are Israel, but those who are of the promise and receive their inheritance by faith. Many of the Jews pursued righteousness by law- keeping rather than by faith. Jesus is referred to as a stumbling block because the only way to receive forgiveness through Christ is by faith, not through obedience to the law. That was offensive to many Jews and caused no small amount of stumbling.
Unfortunately, some of us Christians today find ourselves returning to those same old methods. We get it in our minds that keeping to a set of Christian laws (some biblical and some not) will make us right with God. Not only are we mistaken, but we hinder our growth in Christ with this kind of thinking. We trip over the stone of salvation by grace alone, through faith alone in Christ alone—a rock that ought not to make us stumble, but which is our firm and perfect foundation.