The letter to the Hebrews records that a Believer's foundation is made up of "the first principles of the oracles of God" and "the elementary principles of Christ" (5'11-12 and 6'1-3).
They appear throughout the New Testament. But in chapter six they are listed all together.
The fact is, they came to be listed because the writer had taught them to these Believers once before.
But they had "become dull of hearing". Instead of being teachers of others, he says, they needed to be taught again (chapter 5'11-12).
However, he does not want to say any more about the matter, so he says:
"Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation
of repentance from dead works and
of faith toward God,
of the teaching of immersions,
of laying on of hands,
of resurrection of the dead and
of eternal judgment.
And this we will do if God permits" (chapter 6'1-3) .
One thing about needs to be said here at this point. xx
Thank God for leading the writer to list these wonderful principles for Believers to have and to hold, to explore and to experience.