More passages to consider...
(Heb 2:1-3 NIV) We must pay more careful attention, therefore, to what we have heard, so that we do not drift away. {2} For if the message spoken by angels was binding, and every violation and disobedience received its just punishment, {3} how shall we escape if we ignore such a great salvation? This salvation, which was first announced by the Lord, was confirmed to us by those who heard him.
(Heb 3:7-14 NIV) So, as the Holy Spirit says: "Today, if you hear his voice, {8} do not harden your hearts as you did in the rebellion, during the time of testing in the desert, {9} where your fathers tested and tried me and for forty years saw what I did. {10} That is why I was angry with that generation, and I said, 'Their hearts are always going astray, and they have not known my ways.' {11} So I declared on oath in my anger, 'They shall never enter my rest.'" {12} See to it, brothers, that none of you has a sinful, unbelieving heart that turns away from the living God. {13} But encourage one another daily, as long as it is called Today, so that none of you may be hardened by sin's deceitfulness. {14} We have come to share in Christ if we hold firmly till the end the confidence we had at first.
(Heb 3:19 NIV) So we see that they were not able to enter, because of their unbelief.
(Heb 4:1 NIV) Therefore, since the promise of entering his rest still stands, let us be careful that none of you be found to have fallen short of it.
(Heb 4:11 NIV) Let us, therefore, make every effort to enter that rest, so that no one will fall by following their example of disobedience.
(Heb 6:4-8 NIV) It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, {5} who have tasted the goodness of the word of God and the powers of the coming age, {6} if they fall away, to be brought back to repentance, because to their loss they are crucifying the Son of God all over again and subjecting him to public disgrace. {7} Land that drinks in the rain often falling on it and that produces a crop useful to those for whom it is farmed receives the blessing of God. {8} But land that produces thorns and thistles is worthless and is in danger of being cursed. In the end it will be burned.
(Heb 10:23-27 NIV) Let us hold unswervingly to the hope we profess, for he who promised is faithful. {24} And let us consider how we may spur one another on toward love and good deeds. {25} Let us not give up meeting together, as some are in the habit of doing, but let us encourage one another--and all the more as you see the Day approaching. {26} If we deliberately keep on sinning after we have received the knowledge of the truth, no sacrifice for sins is left, {27} but only a fearful expectation of judgment and of raging fire that will consume the enemies of God.