Let us review Our Lord’s image of the narrow gate, and of what he meant by striving to enter through it.
He was asking us to picture a typical walled city of his time. The great feature of such a city was its main gate. Far from its being a mere gate that swings in and out, it was a courtroom with rows of benches where the heads of families from the town met to transact the business of the town. It was where their contracts were sworn to.
In addition, the gate was the town’s defense. When disease or outlaws threatened the town, the elders at the gate would swing it shut, giving those aught outside no way getting in.
There was, however, one way for a few old timers to get in when the city gates were closed. Around the back of the town, up a rocky hillside, and hidden by brambles, there was a narrow gate. It had its own gatekeeper who would open only to the people of the town who made themselves known to him over the years.
By telling us to enter through the narrow gate Jesus was telling us to avoid taking the easy way that everyone follows. Leading a disciplined life in which we keep in good shape physically, mentally, spiritually is what Jesus means when he tells us to enter through the narrow gate.