In the Sermon on the Mount, the broad way that leads to destruction is the external religious way. The narrow way is the way Jesus taught. This is seen particularly in the “antitheses” section in Mt. 5. For instance, the broad way is by fulfilling the command, “You shall not murder,” but the narrow way is found in Jesus’ statement: “but I say to you, whoever is angry with his brother is guilty…” Or again, “You shall not commit adultery” is the broad way; the narrow way is seen in Christ’s words: “but I say to you that everyone who looks at a woman with lust for her has already committed adultery with her in his heart.”
The broad road is a way of external commands, but the narrow way has to do with something deeper— the changed heart.
The entire sermon demonstrates the contrast between the external religious way and Jesus’ way of righteousness.
Christ ends the sermon with summary statements and challenges. One is this:
“Enter through the narrow gate; for the gate is wide and the way is broad that leads to destruction, and there are many who enter through it. For the gate is small and the way is narrow that leads to life, and there are few who find it.” Mt. 7:13-14
Do you merely perform religious duties like a pharisee, or is your life the fruit of a changed heart? “Unless your righteousness exceeds that of the scribes and the pharisees, you will not enter the kingdom of heaven” (Mt. 5:20)
(jim Elliff, with thanks for the kernel idea for Heather Pentimone during the summer Muller Center Study on The Sermon on the Mount)