This used to be a popular saying, if not a popular practice. The implication used to be that ‘keeping on the strait and narrow’ was to stick to a strict and moral way of life in order to get eternal life. The idea might have had its origin in a misunderstanding of the words of Jesus.
For example, in Matthew chapter 7, Jesus tells his hearers to
“enter through the narrow (strait) gate, because wide is the gate and easy is the way that leads to destruction, and many are they who enter by it. The gate is narrow and the way strait that leads to life, and few are they that find it.”
The confusion might arise because this passage follows on from the golden rule “Everything that you wish men to do to you, you do for them; for this is the law and the prophets.”
Some might conclude from this close proximity that the narrow gate/way is following the golden rule of “doing unto others”, but that is not the case. We have a major problem that can not be fixed by our efforts. Just before the golden rule, Jesus said something very important. Speaking of how God answers prayer, he said “Therefore, if you, who are evil, know how to give good things to your children, how much more your heavenly father…”
Do you see that? Jesus is talking to evil people. People (we) are law breakers – we lie, steal, commit adultery, follow of all sorts of selfish desires and dishonour our parents. Not only are we incapable of doing the golden rule as it ought to be done, but we are evil (despite the fact we give good things to our children).
That is why entering by the narrow gate and following the strait way is not the golden rule which is all the law and prophets. The narrow gate, the narrow way is Jesus Christ himself. If we are to have life, if we are to be one of God’s people, if we are to be saved (Luke 13:23-24), we must rely completely on Jesus Christ: his keeping of the golden rule for us, his dying on the cross to deal with our failure to keep the golden rule, and his resurrection by which he raises people dead-in-sin to life. Entering by the narrow gate is to trust Jesus Christ.
This narrow gate/way is not popular with people. It does nothing for our sinfully constructed self-image. But Jesus is the only way to life eternal. He said, “I am the way, the truth and the life. No one comes to the father except by me.” He is the narrow way because he is the only way.