Because we live in a world of permissive child-rearing...
Because we live in a world of permissive child-rearing, we fail to notice immediately that the basic relationship referred to is the relationship of submission and obedience. The God of the Sermon on the Mount is one to whom people owe submission and obedience. No trinity is mentioned at all. In no place in Matthew five to seven does Jesus even remotely suggest that he himself is God Almighty.
From the Christian point of view the vicarious sacrifice of Jesus on the cross for forgiveness of sin is the heart of the Gospel. Jesus does suggest a condition for forgiveness of sin, but that condition is not his vicarious death on the cross. He says that we shall be forgiven as we forgive (Matthew 6:15), and judged as we judge others (Matthew 7:2). Christians have rightly divided the Sermon on the Mount into three chapters, for it does in fact present three subjects.
Belief in the law and the prophets is the subject of chapter five. Certainty of the Day of judgement is the subject of chapter seven. Chapter six presents the faith of Jesus in practice. Let us first take a look at chapter five. The subject here is to maintain the authority of the law and the prophets. When Jesus spoke to the crowd, he was faced with people who were suspicious of one thing, whether or not he upheld the law. The people had already seen miracles.
They were ready to believe in Jesus provided that he could produce evidence that he was loyal to the lain, and that he upheld the Torah, the books of Moses. This was crucial. Without it he would not be accepted. So Jesus set about the task. First of all he gained the people's confidence by giving a series of blessings. Luke 6:24-26 adds curses to these. The familiar covenant of blessings and curses, so well known from the book of Deuteronomy, immediately flooded into his hearers' minds.
They were on familiar ground. They felt at ease. Then Jesus came to the point. `Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfill. For verily I say unto you, till heaven and earth pass, one jot or one tittle shall in no wise pass from the law, till all be fulfilled.
Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven.' Matthew 5:17-19. There it is: Jesus has had his say. Stronger language could not have been invented.