Galatians 3:8 King James Version (KJV)
8 And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.
John 8:56-58 King James Version (KJV)
56 Your father Abraham rejoiced to see my day: and he saw it, and was glad.
57 Then said the Jews unto him, Thou art not yet fifty years old, and hast thou seen Abraham?
58 Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I am.
I think Abraham had some knowledge.
As for Moses, let us see what scripture says.
John 5:46 King James Version (KJV)
46 For had ye believed Moses, ye would have believed me; for he wrote of me.
John 1:45 King James Version (KJV)
45 Philip findeth Nathanael, and saith unto him, We have found him, of
whom Moses in the law, and the prophets, did write, Jesus of Nazareth, the son of Joseph.
Moses too had some knowledge.
I think you must keep in mind that righteousness has always been by faith, and not works. Salvation by grace through faith. All fall short of God's glory, there is none righteous. This idea that God has some secluded monk, "holy and pure", is a falsehood. For Christ died for the world, every soul. Without Jesus are they not the Lord's children, because they have not been born-again by the Spirit of Adoption (the Holy Spirit).
We have to be careful with speculations, and extrabiblical concepts because they so easily contradict His word, the truth. We may ponder, but one day we will know. Your premise, fellow believer, is false. The people of old too were saved by the means of faith. This faith is in the coming Messiah, or for us, the one Who came and conquered and now sits on the Father's right hand. Jesus Christ. As scripture clearly teaches, those that are saved are saved through His redemptive work. There is no "child" within the Lamb's Book of Life who does not know Jesus.
The significance of evangelists and disciples is testament in and of itself, to the verity of preaching the Gospel in the here and now. For to become a child of God must one be born again, and this process is a result of saving faith in the Lord Jesus Christ.