If Torah (God’s Law) is perfect, how come it missed such a World changing event like the birth of prophet Muhammad (s.a.w.), or the coming of Islam?

If Torah (God’s Law) is perfect, how come it missed such a World changing event like the birth of prophet Muhammad (s. a. w. ), or the coming of Islam?

God’s Law actually foretold the life of prophet Muhammad (s. a. w. ); but it did so only in a cryptic (allegorical) fashion. How so? By means of the story of a great non-Hebrew prophet named “Balaam”. You see, God’s Law (Torah) was purposely written in an ancient form of the Hebrew language; one that had no vowels, as well as very few punctuation marks (no upper case letters, no periods, no question marks, no exclamation signs, etc). And the reason for God to allow His word to lack precision was to keep Torah’s message flexible enough for each of it’s word/phrases/sentences to have multiple interpretations [all of them valid! ].
In our case, the Hebrew name for “Balaam” was shockingly similar to the Hebrew phrase, “B-allah-am”; the latter meaning “with Allah’s people” (or “upon the people of Allah”). You see, Balaam is depicted as “riding” (or “ruling”) upon a wise and noble ass (“ And Balaam rose up in the morning, and saddled his ass, and went with the princes of Moab”- Numberrs 22: 21, King James Bible), just as Muhammad (s. a. w. ) ruled upon the wise and noble children of Ishmael (Allah’s people).
From whence do we know Balaam’s ass was a noble being? From the fact that, though only a simple creature, the ass had a perfect knowledge of Torah’s message-- to abstain from doing harm unto those who have never harmed us (law of “sowing and reaping”). As is written: «And the Lord opened the mouth of the ass, and she said unto Balaam, “What have I done unto thee, that thou hast smitten me these three times? … Am not I thine ass, upon which thou hast ridden ever since I was thine unto this day? was I ever wont to do so unto thee? ”, and he said, “Nay”»- Numbers 22: 28-30, KJB.
And from whence do we know the ass is a symbol of Ishmael (the Arab World)? We know it from the verse that goes on to say, “… Behold thou [art] conceiving, and bearing a son, and hast called his name Ishmael, for י ה ו ה hath hearkened unto thine affliction; and he is a wild-ass man, his hand against every one, and every one's hand against him -- and before the face of all his brethren he dwelleth”- Genesis 16: 11-12, Young’s Literal Translation. In fact, when the book of Joshua mentions that Balaam was killed by the Israelites (“Balaam also the son of Beor… did the children of Israel slay with the sword... ”- Joshua 13: 22, KJB).
Finally, though Balaam was an open enemy of Israel [just as Muhammad was an open enemy of the Jews], yet Balaam’s words contained God’s message true message (“ And Balaam said unto Balak… the word that God putteth in my mouth, that shall I speak ”- Numbers 22: 28, KJB); and the latter might be the reason why our master Moses (peace be upon him) decided to immortalize them by making them part of Torah (book of Numbers, chapters 22 thru 24).

God’s Law hints at the fact that, as long as there is a certain amount of righteous men among any society, the wicked will be spared from God's judgment («And the Lord said [to Abraham], “ If I find in Sodom fifty righteous within the city, then I will spare all the place for their sakes ”»- Genesis 18: 26, King James Bible). But, as soon as those righteous are no longer present, destruction is decreed upon them. As is written: “Run ye to and fro through the streets of Jerusalem, and see now, and know, and seek in the broad places thereof, if ye can find a man, if there be any that executeth judgment, that seeketh the truth; and I will pardon it ”- Jeremiah 5: 1, King James Bible.

If God is O. K. with polygamy, then why was Adam given just one woman?

Scripture states that the Creator has no problem with polygamy. In fact, not only does it state that God was o. k. with king David having multiple wives, but even goes as far as saying it was the Creator who made David acquire king Saul’s former wives. As is written:
“Thus saith the Lord God of Israel, I ANOINTED THEE KING OVER ISRAEL, and delivered thee out of the hand of Saul. AND GAVE THEE THY LORD’S HOUSE, AND THY LORD’S WIVES into thy bosom… AND WOULD MOREOVER (IF THAT HAD BEEN TOO LITTLE) HAVE GIVEN THEE SUCH AND SUCH THINGS”- 2 Samuel 12: 7-8 (1599 Geneva Bible).
But if the former is actually true, then why was Adams given only one wife? Well, in order to understand the answer to this question, we must first ask ourselves the following: Why does God tell us that Eve was created from the part of Adam’s body that is normally populated by multiple ribs (“And the Lord God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof”- Genesis 2: 21, King James Bible)?
What’s the purpose of giving us such particular dertail? It’s purpose is to serve as an allegorical representation of a larger truth-- a way of hinting at the idea that, just as it is perfectly normal for a healthy man to have multiple ribs, so is for a healthy man to have multiple wives.
But if so, why was Adan given one single wife? Why not many? It was done so, in order to promote [and ensure] the brotherhood of all mankind-- In other words, so that [in the future] a man couldn’t say to his neighbor: “I am a descendant of Eve, while you are a descendant of another woman; therefore, since we come from different families, I have no moral obligation to show you any brotherly love”.
And why is brotherly love so important that God is willing to run the risk of making His word appear to be contradictory [seemingly promoting monogamy on one hand, while promoting polygamy on the other hand]? The reason for the former is that God considers brotherly love to be of such paramount importance that everlasting life actually hinges upon it. In other words, wherever brotherly loves is manifested, there will God allow everlasting life to also manifests.
As is written: “HOW DELIGHTFULLY GOOD WHEN BROTHERS LIVE TOGETHER IN HARMONY! IT IS LIKE FINE OIL... FOR THERE THE LORD HAS APPOINTED THE BLESSING—LIFE FOREVERMORE”- Psalm 133, Christian Standard Bible.