Although nowhere explicitly stated, I think Paul is the writer of the Hebrew letter.
His knowledge of the angelic world and his deep insight and explanation of the life and position of the Lord Jesus Christ above the angels, points to that. (C1,2)
Chapter 6 begins with the call, "Therefore.. let us go on unto perfection", after the foundation of Christ has been laid.
The writer then indicates which parts are found in the foundation according to the "doctrine of Christ":
1. Of repentance from dead works.
2. Of faith toward God.
3. Of the doctrine of baptisms.
4. Of laying on of hands.
5. Of resurrection of the dead.
6. Of eternal judgment.
Because the Foundation is divided into 6 subtopics here, I realize the great scope of this topic.
Nevertheless, I want to offer the possibility to say something about some of these 6 points in any order, because they belong inseparably together and together form our foundation Jesus Christ. (1Cor.3:11)
God bless you.