What did Old Testament believers know about Christ's sacrifice?

Is it correct to say that the Old Testament saints had the Gospel preached to them as we know it?

(see Galatians 3:8).

Did Abraham know when he offered up Isaac, that his son was a type of the Son of God? or did Isaiah know when speaking of the sufferings of Christ, that He was the Son of God? or again, did Job know that his Redeemer was the Son of God?

It is not possible, it seems to me, for anyone to search the hearts and understandings of these Old Testament saints, and define the exact extent of their spiritual apprehension of the Person of whom they spake. Spiritual truths are spiritually apprehended.

Certainly the Gospel preached to Abraham was not the Good News as we know it, but it contained it, for its promise of salvation was alone through Christ. Probably the apprehension of Patriarchs and Prophets was much greater than we might naturally suppose. For instance, would it not be difficult to define the limitations of our Lord’s words in John 8:56: “Your father Abraham rejoiced to see my day: and he saw it, and was glad.” This seems to refer to a special occasion, as the verbs are all in the aorist and speak of a point of time in the past, probably to the great deliverance on Mount Moriah. Abraham might have called the name of the place “Jehovah-rahah”__the Lord has provided, had he thought all was over. Evidently he perceived that what had just taken place was the figure of a greater deliverance and so he called it “JehovahJireh”—the Lord will provide. Whether Isaiah and the prophets knew that the Messiah about whom they wrote was to be actually the Son of God, it seems profitless to enquire. They knew they were inspired by the Spirit of Christ testifying in them, and that they were speaking for us, concerning “the sufferings of Christ and the glory that should follow” (1 Peter 1:11). Their difficulty was not to know of whom they spake, but of what manner of time. As for Job’s wonderful words, “I know that my Redeemer liveth,” he would be a bold man (which boldness I neither share nor desire to share), who would undertake to limit this prophecy. It seems to me that in these words God gave His tried servant to understand a bit of “Romans” truth—”My Redeemer”; a bit of “Corinthian” truth —“He shall stand in the latter day upon the earth”; a bit of “Thessalonian” truth—”In My flesh I shall see God”; a bit of “Colossian” truth—”My Redeemer is God”; and a bit of “Timothy” truth—”I know.”