Excellent observation! Amos was prophesying of the downfall of Israel. Israel had always been the source of revelation of God to man, “Surely the Lord God will do nothing, but he revealeth his secret unto his servants the prophets.” (Amos 3:7) It is clear, as you pointed out, that this downfall would happen shortly after the death of Christ. (Amos 8:10)
The prophecy was not necessarily of the ‘downfall of Israel’ (your words, not mine), but of the fulfillment of the Promise of a Savior to be sent by God, that was made to Abraham. Unfortunately, the fulfillment of that Promise, Jesus Christ, was rejected by most of those who were supposed to be waiting for Him. Because they had lost their true faith, they did not recognize the signs of His coming when they happened. Only a very few that were truly faithful did.
Amos 3:7 “[7] For the Lord God doth nothing without revealing his secret to his servants the prophets.” This is from a chapter that also speaks of the fulfillment of the Promise, and of the state of Israel at that time. It also speaks of the punishment that will befall Israel for their sins. God revealed to his prophet (Amos) what would happen, to assure that when the time came they would be well informed of the truth.
Jesus established the true church of Israel with a foundation of apostles and prophets that could guide the church by revelation from God. We enter the Church by repentance and baptism in the name of Jesus Chirst for the remission of sins. (Acts 2:36) This is the new coventant that had been promised to the house of Israel. (Jer. 31:31-34) When we enter this covenant by baptism we “put on Christ” and we also take part in the ancient Abrahamic covenant:
“For ye are all the children of God by faith in Christ Jesus. For as many of you as have been baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise.” (Gal. 3:26-29)
The Abrahamic covenant was passed down through Isaac and Jacob (Israel) and the twelve sons of Israel. The downfall of Israel prophesyed by Amos included the removal of revelation from Israel and therefore the entire world. We learn from Amos 8:11 that the absence of revelation was not a good or normal situation. It was a famine sent from God!
When we ‘put on Christ’ through Baptism, we do become Abraham’s seed and heirs of the Promise, but we do not become part of the Old Covenant in any way. Instead, we become members of the New Covenant of Christ. We are not bound by the Old Law. The New Covenant is based entirely on Christ, so the laws are also different. We are now adopted sons and daughters of God and heirs of Heaven.
The prophecy said that
hearing the word of God would be removed from Israel, not revelation. Jesus
is the Word of God. Israel did not listen to the Word of God then, nor do they hear Him, now. Jesus is the fulfillment of the Old Testament and His coming was the reason for all revelation in the Old Testament. Since He has already come, there is no more need for any new revelations from God. So, the Mormon position that there must always be prophets is wrong.
“John 1:1 In the beginning was the Word, and the Word was with God, and
the Word was God. [2] The same was in the beginning with God. [3] All things were made by him: and without him was made nothing that was made. [4] In him was life, and the life was the light of men. [5] And the light shineth in darkness,
and the darkness did not comprehend it.”