@Charlie24.
Consider this passage:
Therefore let us move beyond the elementary teachings about Christ and be taken forward to maturity, not laying again the foundation of repentance from acts that lead to death, and of faith in God, 2 instruction about cleansing rites, the laying on of hands, the resurrection of the dead, and eternal judgment. 3 And God permitting, we will do so. It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, 5 who have tasted the goodness of the word of God and the powers of the coming age and who have fallen away, to be brought back to repentance. To their loss they are crucifying the Son of God all over again and subjecting him to public disgrace. Land that drinks in the rain often falling on it and that produces a crop useful to those for whom it is farmed receives the blessing of God. 8 But land that produces thorns and thistles is worthless and is in danger of being cursed. In the end it will be burned.
What are these "elementary things"? Repentance from sins, cleansing rites, laying on of hands, the resurrection from the dead, eternal judgment.
These are the things Judaism held, the Hebrew religion that pointed to the Messiah.
Why move on to the maturity of faith?
Because these things have been met in Christ.
How have these people been enlightened, wasted of heavenly things, shared in the Spirit?
The previous chapters in Hebrew tell us. Through Moses, Joshua, the Exodus, God's miracles, all of these things pointing to the coming Promise.
What happens if theses Hebrews return to the elementary things rather than moving to the mature faith?
They look for a fulfillment of the Promise Who has already come and again crucify Christ to themselves. Chrust will not again be crucified, so their faith becomes useless.
The last part of this passage makes this clear:
Land that drinks in the rain often falling on it and that produces a crop useful to those for whom it is farmed receives the blessing of God. But land that produces thorns and thistles is worthless and is in danger of being cursed. In the end it will be burned.
The land drinks in the rain, but some land oroduces a crop and other land thorns. But all of the land drinks in the rain.