I think it's the following:
1. Faith in God.
What is required for salvation? 1. Being a sinner. 2. Hearing the gospel. 3. Receiving what is heard with a humble mind and heart. 4. Believing that Jesus is the Son of God. Believing that Jesus rose from the dead. 5. Making a statement or confession that is in line with what is believed in the heart.
What is required for growing in salvation?.. becoming a mature child of God?
Peter wrote, as babes, desire the sincere milk of God's Word to grow thereby. To the Jew, the Torah is such milk. The Torah is the whole of the old testament. The word Torah has the Hebrew word 'or' in it that directly means 'light'. So, the entrance of God's Word gives light and understanding (discerning, insight) to the simple. The simple are 'the babes'.. the children, the kindergartners.
Only on personal occasions., it's not mandated that every Christian fast.
Jesus suggested that the disciples fast in order to exercise the divine authority needed to cast out a demon.
4. Keeping the ten commandments.
Rom.13 says that Love is the fulfilling of the law therefore applying the ten commandments is Loving others, therefore fulfilling God's law to Love God and Love your neighbor as yourself.
God's way of Love includes walking in His righteousness, peace, and joy.
By no longer having the sin nature through salvation, being a new creature in Christ, having His righteous nature in our hearts.
7. Choosing the good, so you won't sell your soul to the devil.
The soul of the believer is not even up for sale to the devil. The believer belongs to Christ lock, stock and barrel. Though that does not keep the devil from enticing you hook, line and sinker as if you still belong to him.
Yielding to the enticement does not remove your status of salvation. It simply means that you've not resisted the enticement. For that the devil will condemn you as if you've lost your salvation. But he's always a liar.
When we've yielded to our soulish minds to engage in a wrong behavior or a lust of the flesh, our hearts will convict us. That conviction tells us that we are still a child of God. For God disciplines those who are His.
In comparison, the rare case of a mature believer (I use the example of the apostle Paul) would have to renounce their salvation, renounce the Savior Jesus Christ, and completely turn their back on God and His Word. For them there is no way of repentance that they would give that would suffice. Because they have trashed on the blood of Jesus therefore with finality it will no longer work to cleanse them from their unrighteousness of blasphemy.
But such is not the same thing as the believer who isn't mature in their salvation so they yield to the old habits established while unsaved. For those who value the shed blood of Jesus, they can repent of their sins and be cleansed from all unrighteousness and continue to have joy in their salvation through Jesus Christ.