I swore they wouldn't go into their rest

Unbelief is caused by a hardened heart due to the practice of sin and obviously the result is to depart from the living God.
By the word of God we know that God brought the people of Egypt out of servitude and blessed them in the desert so that he fed them with quails and their clothes as they grew their clothes miraculously also grew with them. So they didn't need anything because God took care of them.

However, their ingaratitude and complaining changed the true direction that God had destined for each one and provoked God in the desert because they did not take into account that they had to stand firm in the faith.

Source

And the Bible tells us in Hebrews 3: 16-19 the following:

Hebrews 3: 16-19
16 Who were the ones who, having heard, provoked him? Were not all who left Egypt by the hand of Moses?
17 And with whom was he disgusted forty years? Was it not with those who sinned, whose bodies fell into the desert?
18 And to whom did he swear that they would not enter his rest, but those who disobeyed?
19 And we see that they could not enter because of disbelie (Rv1960)

Recall that the people of Egypt were taken out of slavery by Moses but they provoked God and He was disgusted forty years with them and their bodies fell into the desert because I swear they would not enter their rest because of their unbelief and disobedience.

Recall that the people of Egypt were taken out of slavery by Moses but they provoked God and He was disgusted forty years with them and their bodies fell into the desert because I swear they would not enter their rest because of their unbelief and disobedience.

And for this reason they wandered forty years in the desert, an ungrateful and disobedient people who fell because of their pride.
The call is to take care of our condition before God so as not to lose the promise of entering his rest.

Hebrews 4: 1-3 tells us:
4 Let us fear, therefore, lest the promise of entering his rest still remain, any of you seems not to have attained it.
2 For also the good news has been announced to us as to them; but they did not take advantage of hearing the word, for not being accompanied by faith in those who heard it.
3 But those of us who have believed enter the rest, in the way he said:
Therefore, I swore in my wrath,
They will not enter my rest; m although his works were finished since the foundation of the world.
(RVR1960)

It is important to note that this people constantly heard the word of God and the advice of Moses every day but they were rebellious and did not obey his word.
Likewise, the apostle Paul, through these verses, advises us to fear God so that we may enter into his rest because it is not going to be that we perish for our disbelief and disobedience....

We must be constant and persevere in his word because to us as they have been preached to us the word of God in order to keep it with faith since God swears in his anger that such people would not enter into his rest.