Because.

Romans 4:16
Therefore, the promise comes by faith, so that it may rest on grace and may be guaranteed to all Abraham's offspring--not only to those who are of the Law, but also to those who are of the faith of Abraham. He is the father of us all.

Romans 10:3
Because they were ignorant of God's righteousness and sought to establish their own, they did not submit to God's righteousness.

Matthew 19:16-20
Just then, a man came up to Jesus and inquired, "Teacher, what good thing must I do to obtain eternal life?" . . .

John 6:27-29
Do not work for food that perishes, but for food that endures to eternal life, which the Son of Man will give you. For on Him God the Father has placed His seal of approval." . . .

Acts 16:30-34
Then he brought them out and asked, "Sirs, what must I do to be saved?" . . .

1 John 5:9-12
Even if we accept human testimony, the testimony of God is greater. For this is the testimony that God has given about His Son. . . .

they stumbled.

Romans 11:11
I ask then, did they stumble so as to lose their share? Absolutely not! However, because of their trespass, salvation has come to the Gentiles to make Israel jealous.

Matthew 13:57
And they took offense at Him. But Jesus said to them, "Only in his hometown and in his own household is a prophet without honor."

Luke 2:34
Then Simeon blessed them and said to His mother Mary: "Behold, this Child is appointed to cause the rise and fall of many in Israel, and to be a sign that will be spoken against,

Luke 7:23
Blessed is the one who does not fall away on account of Me."

1 Corinthians 1:23
but we preach Christ crucified, a stumbling block to Jews and foolishness to Gentiles,