The deeper spiritual meaning of Scripture is ALWAYS the more important meaning of a verse.
As a matter of fact, sometimes the plain literal statement on the surface of the verse is impossible to do—leaving only fulfillment through the deeper spiritual meaning:
Deuteronomy 10:16 Circumcise therefore the foreskin of your heart, and be no more stiffnecked.
I would not suggest for anyone to try and literally fulfill this law of God.
If it’s impossible to obey than why did God give this law? Because what's impossible with man is possible with God:
Deuteronomy 30:6 And the LORD thy God will circumcise thine heart, and the heart of thy seed, to love the LORD thy God with all thine heart, and with all thy soul, that thou mayest live.
The Spiritual Meaning is NOT a Secondary Meaning of Scripture, but it is the Primary Meaning of Scripture
"Oh," someone might say, "that's only one verse, you can't overgeneralize and say its true of all Scripture verses."
One verse that disproves the historical grammatical and literal method of interpretation. But if you want more. OK.
Mark 9:43 And if thy hand offend thee, cut it off: it is better for thee to enter into life maimed, than having two hands to go into hell, into the fire that never shall be quenched:
44 Where their worm dieth not, and the fire is not quenched.
45 And if thy foot offend thee, cut it off: it is better for thee to enter halt into life, than having two feet to be cast into hell, into the fire that never shall be quenched:
46 Where their worm dieth not, and the fire is not quenched.
47 And if thine eye offend thee, pluck it out: it is better for thee to enter into the kingdom of God with one eye, than having two eyes to be cast into hell fire:
48 Where their worm dieth not, and the fire is not quenched.
Obviously, Jesus does not want anyone to literally cut off their hand, or foot, or literally pluck out their eye. Something they would do if it were true that the Bible was to be understood in a plain and literal way. But it’s not which means the true and important meaning of Christ's Words can ONLY be found on the spiritual level. Showing us once again that the spiritual meaning is not a secondary meaning of Scripture—it is actually the primary meaning of Scripture.
Here's another example where the deeper spiritual meaning shows itself as the more important meaning, and the meaning God had in view over all.
Genesis 2:17 But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
If we take this verse on its face (plainly) we would think that God did not fulfill His Word. Or worse, that He lied. Adam did eat of the fruit of the forbidden tree, and in the very day he ate—he did NOT die physically. But the Bible indicates that he did die spiritually.
Put this together with all the other Scriptures and you should begin to get the picture that the plain literal meaning, not only is of less significance than the spiritual meaning, but sometimes it (the literal statement) is so unimportant that God doesn't even bother to fulfill it on that level.
Jonah's 40 Days is to be Understood on the Deeper Spiritual Level
Jonah 3:4 And Jonah began to enter into the city a day's journey, and he cried, and said, Yet forty days, and Nineveh shall be overthrown.
People look at this verse and say, God did not destroy Nineveh as He had His prophet Jonah proclaim. It didn't happen.
True. On the plain historical level of things, God did not destroy Nineveh in 40 days.
However, the deeper spiritual meaning is ALWAYS the more important meaning of a verse. And on that level Jonah, whose name means “dove” (and the Holy Spirit is typified in the Bible as a dove) is sent to Nineveh (a type of the world) a second time—and the second outpouring of the Holy Spirit we can pinpoint occurring in the year 1994 AD. Therefore, on a deeper spiritual level God's command to Jonah would not be activated until the year 1994. And from that year a countdown of 40 inclusive years would take place. The year 2033 AD would be the 40th year.
This means that God's warning given to Nineveh, on the deeper spiritual level, which is always the more important level of a Bible verse, is currently in the process of being fulfilled. Jonah (God's elect people) sits under a booth (the feast of tabernacles also known as the feast of the Bible) while the blazing sun (wrath of God being out poured during the entire 40 year period) beats down upon his head (God's elect enduring grief and testing until 40 days expires).