In his letter to the Romans, Paul makes this statement:

But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;
As it is written, Behold, I lay in Sion a stumblingstone and rock of offence: and whosoever believeth on him shall not be ashamed.

Romans 9:31-33

Paul is talking about why so many Jews refuse to submit to Christ. The reason is because they feel their salvation is already attained. The way they see it, they achieve righteousness through obedience to the Law of Moses. Paul however says that salvation comes, not by the Law of Moses, but by faith in Jesus.

And then he quotes from Isaiah and reminds his readers that God laid a stumbling block down that would cause some to be ashamed. What is that stumbling block? It is Jesus!

Jesus Himself is the reason many will perish.

Those who don’t want to submit to Christ will find no other means of salvation available to them. Jesus isn’t going to change His plan of salvation to accommodate those who don’t want to do things His way. Therefore, to those stubborn people, Jesus is a stumbling block. He becomes the very reason why they will go to Hell!

But for the rest of us, who choose to believe on Jesus, for us He is not a stumbling block. He is a source of redemption.

So what is He for you?