Things like repentance, belief, cleanliness, resurrection, and eternal judgement—these are all basic, foundational aspects of Christianity. They are not signs of mature believers.
Some believers squander the immense benefits of the gift of salvation and live in rebellion to God. They fall away from their faith. This does not undo their justification before God, but it ruins their walk and fellowship with God.
Christians are expected to obey God and produce faithful works, which leads to blessings from Him. Some Christians rebel and waste the grace given to them, living lives that are useless and harmful to themselves and others. They will not receive blessings from God.
The Pauline Author is convinced the window of repentance is still open for his friends. He thinks his readers are capable of maturity and faithfulness. He has already seen them show love to God by ministering to other Christians.
God keeps His word. He blesses those who are patient and obedient, like Abraham. This should encourage Christians to pursue maturity. The blessings of living faithfully are a certainty, guaranteed by God.
Jesus is the only priest we need. Like Melchizedek, He is both king and priest, eternal, righteous, who brings peace and blessings. He is the source of our hope, which should keep us from drifting from our faith.
Paul wants his audience to grow up as believers. They already know the basic elements of Christianity, and they need to mature in their faith. Paul believes his readers are capable of maturity, but he warns them that some believers wander away from God and lose blessings. He emphasizes how faithful God’s word is, and that He blesses His children who are obedient toward Him and become mature.