The Old Testament Hebrew Manuscripts foretold of the ‘first’ coming of Messiah Jesus Christ; His birth, His Mission, and how He would suffer on the cross. So why don’t the majority of Jews believe that Christ came and fulfilled that Mission as Savior, especially since those Jews are in possession of The Hebrew Manuscripts?

The reason many of the ‘house of Judah’ today, i.e. Jews, still haven’t accepted Jesus Christ as Messiah, believe it or not, was and is part of God’s Plan. Well why would God do that to His People? Consider what Peter says:

1 Pet 2:7-10
7    Unto you therefore which believe He is precious: but unto them which be disobedient, the Stone Which the builders disallowed, the same is made the head of the corner,
8    And a Stone of stumbling, and a Rock of offence, even to them which stumble at the word, being disobedient: whereunto also they were appointed.
9    But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of Him Who hath called you out of darkness into His marvellous light:
10    Which in time past were not a people, but are now the people of God: which had not obtained mercy, but now have obtained mercy.
(KJV)

     Peter is letting us know that the ‘nations’ who accepted Christ as Savior, at one time ‘were not a people’ of God. This has much to do with the ‘house of Israel’, i.e. the Ten Tribes (remember Loammi=not My People), being scattered among the Gentiles, and both accepting Christ Jesus as Savior when they heard Him preached by the Apostles of Christ.
     The ‘house of Judah’ stumbled at The Cornerstone (Christ) Which they rejected. In 1 Peter 2:7-8 he says the Jews were ‘appointed’ to this stumbling at Christ’s Word, but not the Jews only. Paul in Romans Chapters 9 through 11 tells us why – so that many of the Gentiles who believe, which “were not a people”, might be ‘grafted’ into the same ‘tree’ of God’s People. The Jews are blinded so that Salvation through Jesus Christ would be full and more complete. Paul also tells us in Romans 11 that any of the Jews who now accept Christ Jesus, are grafted in now; but the majority of Jews will not be joined with Christ until the ‘fullness of the Gentiles’ is whole (Rom.11:23-28). That means there is still yet hope for them.
     God is causing that ‘slumber’ of not having ‘eyes to see and ears to hear’. We Gentiles should not get too cocky about having accepted Jesus as Savior over those of the ‘house of Judah’ which haven’t. You know why?

Isa 8:13-15
13    Sanctify the LORD of hosts Himself; and let Him be your fear, and let Him be your dread.
14    And He shall be for a sanctuary; but for a stone of stumbling and for a rock of offence to both the houses of Israel, for a gin and for a snare to the inhabitants of Jerusalem.
15    And many among them shall stumble, and fall, and be broken, and be snared, and be taken.
(KJV)

     The Cornerstone (Jesus Christ) is “…a stone of stumbling and for a rock of offence to both the houses of Israel…”. That’s talking about those of the ‘house of Israel’ today also, the Western Christian Nations, who have received Jesus Christ as Messiah. It applies to both Judah and Israel (Ten Tribes). “How could they ‘stumble’ if they’ve already accepted Christ,” one might ask? By worshipping the wrong messiah of our near future, that’s how! Satan is coming first as a ‘false Messiah’, claiming to be Christ (Immanuel–‘God with us’), sitting in the Temple of God (II Thess.2; Ezek.28;31; Isa.14). Our True Savior Jesus Christ will return on the ‘last trump’ to defeat Satan, all in our near future.
     Which is worse; to seek Salvation through following God’s Law without faith in Christ, still waiting for His first coming, as the majority of the Jews do; or to accept and believe on Jesus Christ, yet mess up later when Satan comes, and worship him as a fake Messiah, thinking he’s Christ? That’s what Isaiah 8:15 means with being ‘snared’ and ‘taken’! The first one ‘taken’ in the field is by Antichrist (compare Luke 17:36-37 with Matthew 24:28). So the deception is not only ‘appointed’ to many of Judah, no…but to many who once believed on Christ also, who will become ‘apostate’, falling away by worshipping a false Messiah.
     So why can’t both the Jew and Gentile who stumble, just wake up, out of their spiritual slumber? Because God is allowing the deception by the ‘workers of iniquity’, i.e. the sons of Cain or Kenites, who are so…strong today, that many don’t even have a chance. Satan and his children are God’s ‘rod’ of correction to His People. Once the Christian starts to understand God’s Message through His Old Testament prophets, about Satan being controlled by God, then our Father’s greater Plan begins to unfold, and an understanding that He is in charge is revealed. Until that Truth is grasped, the elect may find it difficult to deal with the sorrow we feel for our lost brethren who stumble (from both ‘houses’). Those who remain ignorant of that Plan fight against each other. 
     So why is God allowing all this ‘deception’, even towards ‘both’ houses of Israel? Our Father is going to show His Power and Supreme Authority to us, while revealing how silly, ignorant, and uncaring about Him, His children can be. No other Glory anywhere, will compare with this future event of Christ’s coming. The ‘shock value’ will be enormous! But not for those who are watching, as our Savior commanded.
     But God has preserved a ‘remnant’ who shall know His Truth, and will not be swayed from Christ by accepting the false Messiah. Even His preservation of His elect is by ‘appointment’! Our Father is in control, guiding the ‘helm’ with utmost sureness. I have total confidence in God and His Son, and as to the directions of His Plan He has given us, all according to His Word. Give thanks and praise to Him through Christ if you know what I’m talking about, for we are as ‘filthy rags’.
     So what do we do in the meantime? Teach, teach, teach God’s Word. Drop a ‘seed’ of our Father’s Truth to those who stumble. Be bold when given the chance. Learn The Word using common sense, and teach It using common sense in ‘plain’ language. Good honest folk exist everywhere in the world, and they live plainly by common sense.