The writer continues with warnings not to disbelieve. We must not harden our heart by practicing error and sin and ignoring the Scriptures rules. There are sad consequences to making God angry by our lapse into errors of doctrine and actions of doing sins when we know we are wrong.
We need to walk in truth. See Psalm 86:11, 1 John 1:6, and 3 John 1:4.
My translation and notes of Hebrews 3:14-19
14 For we have been made partakers of Christ, if we hold on to the beginning of our confidence firmly to the end.
[The Greek word for partakers is μέτοχος métochos (G3353). It means to share in something, a partaker. Compare Luke 5:7. The Greek word for hold is κατέχω katéchō (G2722). It means to firmly grasp. Compare Matthew 21:38. This is a conditional sentence—IF. The “if” is to have a will to continue in the faith. We do not want to fall away from the faith (Hebrews 3:12). We do want the assistance of our brothers and sisters in the faith (Hebrews 3:13) and want to persevere in the faith (v14). God’s grace continually assists us. Compare Luke 8:15].
15 That’s why it is said, “Today—if youp will listen to his voice—do not harden yourp hearts as in ’The Provocation.’” [Psalm 95:7-8]
[Most people live as they will live for decades, but reality is different. Life may end at any time. All humans must believe while they are still alive—which is today. If there is no belief, there are no blessings].
16 For some, after they had heard, did provoke to anger, but not everyone who came out of Egypt with Moses.
17 But with whom was he exasperated with for forty years? Wasn’t it with those who had sinned, whose carcasses fell in the wilderness?
[Sin and unbelief have consequences (Numbers 12). All that Israel experienced in their deliverance from Egypt was willfully ignored].
18 Or to whom was it that he took an oath that they wouldn’t enter his rest? Wasn’t it with those who refused to believe?
19 So we see that they could not enter because of unbelief.
[These individuals who refused to believe God and God’s chosen spokesman—Moses—had judgment and sentence executed by the Judge of all judges. The very promise these people rejected. This is a principle and warning to all. If we refuse to believe, we will suffer God’s wrath].