Compare to Revelation
DEU.31.6
Revelation proclaims that the cowardly are first on the list to lose access to Yahwehs kingdom.
Revelation 21:8
But for the cowardly, unbelieving, sinners, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars, their part is in the lake that burns with fire and sulfur, which is the second death.”
These were all the same reasons the Israelites who died in the desert weren't allowed into the promised land. They trusted more in what they saw in the world, than what they experienced as blessings from Yahweh. They were never satisfied with what they had. They refused to see the love, beauty and bounty that their God provided; and instead lusted for the things they didnt have. They coveted their neighbors.
Our God requires us to be bold and courageous. To love Him fiercely, and to stand strong in what he tells us.