Jesus’ analogy of the kingdom of God being like a grain of mustard seed made it seem as if there would be only a small number people that would make it into heaven (Luke 13:19). Therefore, someone asked him, “Lord, are there few that be saved?” (Luke 13:23). Jesus’ response made it clear that the limitation to getting into heaven was not because of the size of God’s kingdom, but the method by which people would have to enter into it. He said, “Strive to enter in at the strait gate: for many, I say unto you, will seek to enter in, and shall not be able” (Luke 13:24). Jesus previously referred to the strait gate in his Sermon on the Mount in which he said:
Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat: because strait is the gate, and narrow is the way, which leadeth to life, and few there be that find it. (Matthew 7:13-14)
The Greek word translated narrow, thlibo (thlee-bo) has to do with a path of life that is filled with trouble and suffering (2346). What Jesus was saying was that most people wouldn’t chose the strait or narrow gate because it runs counter to our natural instincts. Jesus further illustrated this point when he said, “And behold, there are last which shall be first, and there are first which shall be last” (Luke 13:30). The Greek terms Jesus used for first and last suggest he was describing a processional or steady stream of people going through the gates of heaven. In this processional those who started out at the end of the line might get in first due to their effort to enter the gate as quickly as possible. Others who were at the head of the line, but hesitated to go through the gate (i.e. experience suffering in their lives), might not make it in because the doors would eventually be shut (Luke 13:25).
Jesus’ instruction to “strive to enter in at the strait gate” (Luke 13:24) may have been a reference to spiritual warfare. The Greek word translated strive, agonizomai (ag-o-nid´-zom-ahee) means to struggle and is literally translated “to compete for a prize” (75). Figuratively, agonizomai means to contend with an adversary. Satan is sometimes referred to as our adversary (1 Peter 5:8) and the Apostle Paul talked about spiritual warfare in the context of wrestling “against principalities, against powers, against the rulers of darkness of this world, against spiritual wickedness in high places” (Ephesians 6:12). Something that Jesus seemed to want his listeners to understand was that the strait gate couldn’t be entered into without expending some effort. In the illustration he used of the master of the house rising up and shutting the door unexpectedly, Jesus said of those that didn’t make it in, “Then shall ye begin to say, We have eaten and drunk in thy presence, and thou hast taught in our streets. But he shall say, I tell you, I know you not whence you are; depart from me, all ye workers of iniquity” (Luke 13:26-27).