Christ is drawing the line as clearly as possible between the way that leads to destruction and the way which leads to life.
The wide gate includes all religions of works and self-righteousness, with no single way, but it leads to hell, not heaven.
Commentary from the MacArthur study Bible, notes for Matthew 7:13-29.
Christ continually emphasized the difficulty of following Him (Matthew 10:38; 16:24,25; John 15:18,19; 16:1-3). The narrow gate is by faith, only through Christ, constricted and precise.
Salvation is by grace alone, but is not easy. It calls for knowledge of the truth, repentance, submission to Christ as Lord, and a willingness to obey His will and Word.
Commentary from the MacArthur study Bible, notes for Matthew 7:13, 14.