Two Ways

Setting and Overview
After the ethical instructions conclude with the Golden Rule in Matthew 7:12, Jesus then ends the Sermon on the Mount with four different illustrations of the difference between entering the kingdom and failing to do so. Speaking those who have demonstrated at least a nominal commitment to following and obeying Him, and after giving instruction regarding what is expected of those who are in the kingdom, it is likely that most of those who were listening believed that they were ready to accept the expectations that came along with being a follower of Jesus and assumed that they were on a path to security in it. Jesus here describes in four different, but complementary, ways the difference between the two ways.

Exposition
The first comparison is between two gates and paths. Deuteronomy 30:15-19 would have likely come to mind to His listeners, and possibly Psalm 1:1-2, Joshua 24:15 and others, but the description is different and the focus here is on eternal spiritual results, rather than earthly consequences. One path and gate look easy and appealing, and thus many take it. The other set looks difficult and few seek it out. Their ends, however, are reversed as the difficult path leads to fullness of life and the other leads to destruction. Following so closely after Matthew 6:19-34, some of the focus was likely on the difference between pursuing the world and trying to add obedience to Jesus on top (the wide gate) versus forgoing the pursuit of the world and instead taking up our cross and following Him (the narrow.)
False prophets are described in fuller detail in other places, as are the instructions for how to identify and avoid them (II Corinthians 11:12-15, II Peter 2, I John 4:1-3, I Timothy 6:5-6, Colossians 2:8, Galatians 1:7.) As with in those other passages, the focus is on teachers who simply make mistakes, are immature, have doctrinal errors, or even fall into disqualifying sin (although those, especially the latter, should be addressed as well.) The focus here is those who deny the Gospel, intentionally deceiving others for their own gain. The focus here is likely on those who would deceive people into taking the wide path in order to gain popularity, wealth, and/or power. Ultimately they will be shown to be who they are through their fruit, which may refer in part to their lifestyles (II Peter 2:2) but probably focuses more on the result of their ministry as seen in the spiritual growth and maturity of those who are under their teaching.
Some of those teachers may be in mind in verses 21 through 23. Even some of those who identify and proclaim Christ as Lord, who have performed powerful miracles and works in His name may not actually belong to Him. Jesus says to them that He never knew them and calls them “lawbreakers,” which refers specifically to those who completely reject the law. So, the picture here is of nominally effective ministers who nonetheless rejected Christ’s authority of their own life and instead sought their own benefits.
The final picture is of two builders and houses. One is built on sand and appears to be stable for a while, but eventually the sand is washed away and the house is destroyed. The other builder dug down to bedrock, a more difficult process and one that is tempting to forego, but it ultimately survives the test. The focus here is not on the building itself (the acts of righteousness) but rather the foundation (our motivation.) 6:1-18 comes to mind here, as we see the difference between doing acts of piety to impress men versus out of obedience to God.

Examination and Application
Ultimately Jesus is calling us to choose, and to commit, rightly. This is not a grading scale of righteousness, with only a few percent doing enough good things to earn eternal life. Rather, this is reminding us that none of us will pass the test based on our own righteousness, and it is only by grace through faith, as we are judged by Christ’s righteousness, that we are seen to be worthy to enter into His kingdom. Too many will fail to recognize that, and instead think that they only need some grace, and thus only need to commit partially to Christ and retain the freedom to pursue the world the rest of the time. That mindset is the wide path that leads to destruction, building on sand with the belief that it will be strong enough to hold. Any who would teach that are false prophets, and those who believe them, along with the false prophets themselves, will be revealed as those who Christ never truly knew.