Romans 2:4

Or, do you despise the abundance of God's kindness and tolerance and patience [toward you], not realizing that His kindness is intended to cause you to repent? [i.e., to change your hearts and lives].

Romans 11:20

True, but they [i.e., the Jews] were [really] broken off because they did not believe [in Christ], and you [Gentiles] remain [in God's favor] because you do believe [in Him]. So, do not become arrogant [about it], but be fearful.

Hebrews 4:1

So, as long as God's promise of entering into a state of rest with Him [still] remains, we should fear that someone among you will appear [in the end] to have fallen short of [attaining] it. [Note: In this section "entering into rest" refers to Israel entering Canaan (verses 6, 8) and to Christians entering heaven (verses 3, 9). The "Sabbath day rest" is represented as a type of both].

1 Peter 1:17

And if you call upon [God as] your Father, who judges each person's work impartially, [then] conduct yourselves during the time you spend in this life showing reverence [to God].

Treasury of Scripture Knowledge

Summary

Happy is the man that feareth alway: but he that hardeneth his heart shall fall into mischief.

General references

Bible References

Happy

Romans 11:20
True, but they [i.e., the Jews] were [really] broken off because they did not believe [in Christ], and you [Gentiles] remain [in God's favor] because you do believe [in Him]. So, do not become arrogant [about it], but be fearful.
Hebrews 4:1
So, as long as God's promise of entering into a state of rest with Him [still] remains, we should fear that someone among you will appear [in the end] to have fallen short of [attaining] it. [Note: In this section "entering into rest" refers to Israel entering Canaan (verses 6, 8) and to Christians entering heaven (verses 3, 9). The "Sabbath day rest" is represented as a type of both].
1 Peter 1:17
And if you call upon [God as] your Father, who judges each person's work impartially, [then] conduct yourselves during the time you spend in this life showing reverence [to God].

General references

1 Corinthians 10:12
So, the person who thinks he is standing firm [in the faith] should pay attention [to his life], so that he does not fall [away from God].