To your opening question in the title of this thread, "Was the Cross Always Understood?," the need for atonement was always understood. Whether or not everyone understood that the atonement would come by the means of the cross is another question. There certainly were glimpses of the cross in the Old Testament. The serpent on the pole immediately comes to mind (Num. 21:8-9, John 3:14-15), and the psalmist foretold of death by crucifixion in Psalm 22:14-18. We also catch of glimpse of Christ becoming a curse for us on the cross in Deuteronomy 21:22-23 (Gal. 3:13).
Amen, good post! And speaking of which, we might be able to catch another similitude of the cross
Gen 2:22 And he said, Take now thy son, thine only son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of.
And Abraham went, him seeing before
Gen 22:3 Then on the third day Abraham lifted up his eyes, and saw the place afar off.
Gen 22:6 And Abraham took the wood of the burnt offering, and laid it upon Isaac his son; and he took the fire in his hand, and a knife; and they went both of them together.
Gal 3:8 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.
Heb 11:13 These all died in faith, not having received the promises , but having seen them afar off, and were persuaded of them, and embraced them, and confessed that they were strangers and pilgrims on the earth.
Heb 11:17 By faith Abraham, when he was tried, offered up Isaac: and he that had received the promises offered up his only begotten son,
Heb 11:18 Of whom it was said, That in Isaac shall thy seed be called:
Heb 11:19 Accounting that God was able to raise him up, even from the dead; from whence also he received him in a figure.
Acts 10:40 Him God raised up the third day, and shewed him openly
Similarly here Isaac asks,
Gen 22:7 And Isaac spake unto Abraham his father, and said, My father: and he said, Here am I, my son. And he said, Behold the fire and the wood: but where is the lamb for a burnt offering?
Gen 22:8 And Abraham said, My Son, God will provide himself a lamb for a burnt offering: so they went both of them together.
And since the law having shadow of the good things to come and not the very image of things, we see in John
John 1:36 And looking upon Jesus as he walked, he saith, Behold the Lamb of God!
The lamb of God, or as God providing himself a lamb
Romans 8:2 He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things?
Shows a similitude of the only begotten Son of God, in the picture of Isaac and Abraham (Gen 22:2) and since Abraham is a prophet God spake by the same using similitudes by them.
Hosea 12:10 I have also spoken by the prophets, and I have multiplied visions, and used similitudes, by the ministry of the prophets.