2 Nephi 9:27–38 Nephi's now grown up little brother, Jacob, continued to teach many gospel principles, such as our attitudes and actions can prevent us from receiving the blessings of the Atonement.
Our life on earth is our mortal probation, where we are tested and tried to see if we will repent, choose the better part, and be faithful to God, The Father, and The Son, Jesus Christ 2 Nephi 2:21; 2 Nephi 2:30; Mormon 9:28. Jacob warns against transgressing the commandments and wasting the days of our probation 2 Nephi 9:27. Choosing iniquity and not repenting, we waste the days of our probation 2 Nephi 9:38; Alma 34:31–33; Helaman 13:38.
In our 'great' wisdom, we may think our learning and riches are better than worshipping God. We may choose idols of all sorts above God 2 Nephi 9:28–30, 37. The pursuit of knowledge and riches are not bad in themselves if we remember all knowledge comes from God and use riches to bless the lives of others 2 Nephi 9:29; Jacob 2:18–19.)
When we get caught up in worldly pursuits and set aside the things of God, we become spiritually deaf and blind 2 Nephi 9:31–32. The way to return to a worshipful life or open our ears and eyes to the truths of the gospel is to accept Jesus' gifts of the Atonement, pray always, feast upon His word, and follow Him.
Circumcision was a sign that a man had covenanted with God before Jesus fulfilled the law Genesis 17:11, 14. Being “uncircumcised of heart” symbolically means to be hard heartedly break our covenants with God 2 Nephi 9:33.
Our Father and His Son allow no lying and committing murders and whoredoms and abhor these sins 2 Nephi 9:34–36.
Once again the who thing boils down to this. The Atonement can only work in our lives if we accept it and live by and defend the doctrines and ordinances of the gospel of Jesus Christ. To do this, we need to LEARN and KNOW what those doctrines and ordinances include through feasting on the words of Christ, repent and accept His grace and forgiveness, worship Him formally, live by the inspiration of the Holy Ghost, and develop a relationship with our Lord through prayer.