http://www.gotquestions.org/before-Jesus.html
Question: "How were people saved before Jesus died for
our sins?"
Answer: Since the fall of man, the basis of salvation has
always been the death of Christ. No one, either prior to the cross
or since the cross, would ever be saved without that one pivotal
event in the history of the world. Christ's death paid the penalty
for past sins of Old Testament saints and future sins of New
Testament saints.
The requirement for salvation has always been faith. The object of
one's faith for salvation has always been God. The psalmist wrote,
“Blessed are all who take refuge in him” (Psalm 2:12). Genesis 15:6 tells us that
Abraham believed God and that was enough for God to credit it to
him for righteousness (see also Romans 4:3-8). The Old
Testament sacrificial system did not take away sin, as Hebrews 10:1-10 clearly
teaches. It did, however, point to the day when the Son of God
would shed His blood for the sinful human race.
What has changed through the ages is the content of a believer's
faith. God's requirement of what must be believed is based on the
amount of revelation He has given mankind up to that time. This is
called progressive revelation. Adam believed the promise God gave
in Genesis 3:15 that the Seed of
the woman would conquer Satan. Adam believed Him, demonstrated by
the name he gave Eve (v. 20) and the Lord indicated His acceptance
immediately by covering them with coats of skin (v. 21). At that
point that is all Adam knew, but he believed it.
Abraham believed God according to the promises and new revelation
God gave him in Genesis 12 and 15. Prior to Moses, no Scripture was
written, but mankind was responsible for what God had revealed.
Throughout the Old Testament, believers came to salvation because
they believed that God would someday take care of their sin
problem. Today, we look back, believing that He has already taken
care of our sins on the cross (John 3:16; Hebrews 9:28).
What about believers in Christ's day, prior to the cross and
resurrection? What did they believe? Did they understand the full
picture of Christ dying on a cross for their sins? Late in His
ministry, “Jesus began to explain to his disciples that he must go
to Jerusalem and suffer many things at the hands of the elders,
chief priests and teachers of the law, and that he must be killed
and on the third day be raised to life” (Matthew 16:21-22). What was the
reaction of His disciples to this message? “Then Peter took him
aside and began to rebuke him. ‘Never, Lord!’ he said. ‘This shall
never happen to you!’” Peter and the other disciples did not know
the full truth, yet they were saved because they believed that God
would take care of their sin problem. They didn't exactly know how
He would accomplish that, any more than Adam, Abraham, Moses, or
David knew how, but they believed God.
Today, we have more revelation than the people living before the
resurrection of Christ; we know the full picture. “In the past God
spoke to our forefathers through the prophets at many times and in
various ways, but in these last days he has spoken to us by his
Son, whom he appointed heir of all things, and through whom he made
the universe” (Hebrews 1:1-2). Our salvation
is still based on the death of Christ, our faith is still the
requirement for salvation, and the object of our faith is still
God. Today, for us, the content of our faith is that Jesus Christ
died for our sins, He was buried, and He rose the third day
(1 Corinthians 15:3-4).