The Corinthians had already been lectured about their need to grow up (spiritually): they should have been well past needing teaching the basics.
Now it was the turn of the Jewish Christian community:
Hebrews 5:12-14 You have been believers so long now that you ought to be teaching others. Instead, you need someone to teach you again the basic things about God’s word. You are like babies who need milk and cannot eat solid food. For someone who lives on milk is still an infant and doesn’t know how to do what is right. Solid food is for those who are mature, who through training have the skill to recognize the difference between right and wrong.
So what are the basics?
Hebrews 6:1-2 So let us stop going over the basic teachings about Christ again and again. Let us go on instead and become mature in our understanding. Surely we don’t need to start again with the fundamental importance of repenting from dead works and placing our faith in God. You don’t need further instruction about baptisms, the laying on of hands, the resurrection of the dead, and eternal judgment.