Hebrews 4:2 For good news came to us just as to them, but the message they heard did not benefit them, because they were not united by faith with those who listened.
1 Corinthians talks about the good news, the gospel of Christ preached to ancient Israel.
10:1 For I want you to know, brothers, that our fathers were all under the cloud, and all passed through the sea, 2 and all were baptized into Moses in the cloud and in the sea, 3 and all ate the same spiritual food, 4 and all drank the same spiritual drink. For they drank from the spiritual Rock that followed them, and the Rock was Christ.
Same gospel; same promise; same eternal purpose.
WARNING TO US ALL
What the writer in Corinthians and Hebrews point out is that though the promise is sure, beware that you don't come up short by not continuing to trust in Christ as they did and fell in the wilderness. God issued another promise to the adults that he brought out of Egypt - you will never enter my rest.
If you are a Christ follower stay humble because
Romans 9 says,
17 But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, 18 do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. 19 Then you will say, “Branches were broken off so that I might be grafted in.” 20 That is true. They were broken off because of their unbelief, but you stand fast through faith.
So DO NOT BECOME PROUD BUT FEAR. 21 For if God did not spare the natural branches, neither will he spare you. 22 Note then the kindness and the severity of God: severity toward those who have fallen, but God's kindness to you, PROVIDED YOU CONTINUE IN HIS KINDNESS.
The promise of salvation through Christ is sure; salvation is NOT a fragile thing but Hebrews 4:1 says
4:1 Therefore, while the promise of entering his rest still stands, let us fear lest any of you should seem to have failed to reach it.
Again 1 Corinthians 10
6 Now these things took place as examples for us, that we might not desire evil as they did. 7 Do not be idolaters as some of them were; as it is written, “The people sat down to eat and drink and rose up to play.” 8 We must not indulge in sexual immorality as some of them did, and twenty-three thousand fell in a single day. 9 We must not put Christ to the test, as some of them did and were destroyed by serpents, 10 nor grumble, as some of them did and were destroyed by the Destroyer. 11 Now these things happened to them as an example, but they were written down for our instruction, on whom the end of the ages has come. 12 Therefore let anyone who thinks that he stands take heed lest he fall. 13 No temptation has overtaken you that is not common to man. God is faithful, and he will not let you be tempted beyond your ability, but with the temptation he will also provide the way of escape, that you may be able to endure it.