We know that Jesus came to die on the cross bearing the penalty of our sin. But we also know the death of Christ happened at a specific point in time. Many Christians wonder how those who lived before the time of Christ were saved or if eternal life for them was a possibility.
There are many who believe that before the time of Christ, people were saved by keeping the Law. However, if you carefully read the Old Testament you find that among the promises outlined for obedience there was never a promise of heaven. This is confirmed in the New Testament in passages such as Romans 3:20, which says: "Therefore no one will be declared righteous in his sight by observing the law..." (NIV)
In Ephesians 2: 8-9 the Apostle Paul reminds us that we are saved by grace through faith. He says that salvation is not a work of our own effort or merit, but is instead "the gift of God." Although this is what we refer to as "the Gospel" (which means good news), there is no reason to believe the way of salvation has ever been different. Faith in God has always been the key.
As far back as Genesis chapter 15, we're told that Abraham "...believed the LORD, and [God] credited it to him as righteousness." Genesis 15:6 (NIV) And in the Psalms we see that God has always been communicating to His people that "Blessed are all who take refuge in him." Psalm 2:12 (NIV)
People who lived and died before Christ had to trust God and rely on His mercy just like we do. Their faith looked forward to Christ's work on the cross while ours looks backward. I'm not suggesting they had the full picture of God's redemptive program — not by a long shot. Their faith was based on the amount of revelation they had been given.
The important thing to remember is that there has never been a different way to be saved other than placing one's faith completely in God's mercy.