This verse is full of wordplay and humor. It uses a lot of Jesus's forms of humor including exaggeration, double meanings, repeating words, and so on. This is all lost in translation. The beginning of this verse ("Woe to you") is repeated many times in the following verses. It is hard to imagine this working as a lecture, but, if we think of it in a lighter vein ("boo-hoo to you"), the repetition itself is a form of humor. This first verse sets the comedic tone for a series of verses, while certainly critical, they are also really extremely playful.
The most interesting philosophical aspect of this verse is the first two occurrences of the Greek verb translated as "go in" and "enter." They are not in the active voice but either the passive or middle voice. So people are either show into the realm, which seems a good description of Jesus's mission, or they show themselves in, a good description of the personal nature of the journey. They do not simply "go in" or "enter in." In looking at other uses of this word to describe entering the "kingdom," I find middle voice examples (Matthew 19:23, Matthew 7:21, Mark 10:23) but no passive examples. Most occurrences are active but either as subjunctive or infinitives. The most likely meaning seems the middle voice.