God is serious! The penalty for rejecting God's teaching, for not learning, is that we will be barred from becoming priests, the Christian's promised vocation if he enters the Kingdom of God (see Revelation 5:10).
God says something similar in Leviticus 26:23-24: "If after all of this punishment you still do not listen to me, but continue to defy me, then I will turn on you and punish you seven times harder than before" (Today's English Version). The key phrase here is "if you still do not listen to me." We must not fail to heed God.