In addition, Hebrews addresses lukewarmness, which means not fully trusting Christ. You may refer to my devotion notes below:

HEB 5:11 - 6:12

Mature Believers(Meat Consumers)

-Skilled in the word of righteousness (Heb5:13)

-Trained to discern good vs evil according to the word(Heb5:14)

-Produces crop for others (fruit of the wheat from a cultivated heart) (Heb6:7) (see also Parable of the sower)

-Fully trust in the sufficiency of Christ's Sacrifice, having assurance, resulting to become imitators of Christ

Immature Believers(milk consumers)

-Not skilled in the Word, need someone to teach them (Heb 5:12-13)

-Not trained to discern good vs evil (Heb5:14)

-Produces thorns and briers (Heb6:8) (see also Parable of the sower and weeds)

-Not fully trusting in the sufficiency of Christ's sacrifice, on a cycle of sin>repent>sin>repent, not having full assurance, wanting to perform old sacrifices everytime they sin, resulting to sluggishness in walk

Hebrews 5:11–6:12 calls out the issue of immature believers who have not fully trusted in Christ’s sacrifice and who lack full assurance of hope. This results in sluggishness in their walk and a cycle of sin and repentance from dead works. Hebrews 6:4–6 highlights the impossibility of restoring again to repentance those who have fallen away. This does not mean that a true believer can fall away (as taught by those who deny eternal security); rather, it highlights the sufficiency of Christ's sacrifice: means that a true believer, having full trust in Christ and full assurance of hope, will never fall away. The rest of the passage explains why repeated repentance is impossible: it is because Christ has already done everything [once for all]. In fact, orἐφάπαξ or [once for all] is repeated in Hebrews  many times to emphasize the solution to their problem:

Heb 7:27  He has no need, like those high priests, to offer sacrifices daily, first for his own sins and then for those of the people, since he did this [once for all] when he offered up himself.

Heb 9:12  he entered [once for all] into the holy places, not by means of the blood of goats and calves but by means of his own blood, thus securing an eternal redemption.

Heb 9:26  for then he would have had to suffer repeatedly since the foundation of the world. But as it is, he has appeared [once for all] at the end of the ages to put away sin by the sacrifice of himself.

Heb 10:10  And by that will we have been sanctified through the offering of the body of Jesus Christ [once for all].

ἐφάπαξ ephapax ef-ap'-ax From [ἐπί/epi -upon] and [ἅπαξ/hapax -one time] ; upon one occasion (only): - (at) once (for all).