Some people tend to think that, in the Old Testament, people were saved by obeying the Ten Commandments (i.e., by works) and in the New Testament, people are saved by believing in Jesus (i.e., by faith).
And yet, Hebrews 11 states that those in the Old Testament were actually saved by faith. They believed God and looked forward to the coming of the promised Messiah:
“Now faith is being sure of what we hope for and certain of what we do not see. This is what the ancients were commended for. By faith we understand that the universe was formed at God's command, so that what is seen was not made out of what was visible.
By faith Abel offered God a better sacrifice than Cain did. By faith he was commended as a righteous man, when God spoke well of his offerings. And by faith he still speaks, even though he is dead.
By faith Enoch was taken from this life, so that he did not experience death; he could not be found, because God had taken him away. For before he was taken, he was commended as one who pleased God. And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.
By faith Noah, when warned about things not yet seen, in holy fear built an ark to save his family. By his faith he condemned the world and became heir of the righteousness that comes by faith.
By faith Abraham, when called to go to a place he would later receive as his inheritance, obeyed and went, even though he did not know where he was going. By faith he made his home in the promised land like a stranger in a foreign country; he lived in tents, as did Isaac and Jacob, who were heirs with him of the same promise. For he was looking forward to the city with foundations, whose architect and builder is God. By faith Abraham, even though he was past age—and Sarah herself was barren—was enabled to become a father because he considered him faithful who had made the promise. And so from this one man, and he as good as dead, came descendants as numerous as the stars in the sky and as countless as the sand on the seashore.
All these people were still living by faith when they died. They did not receive the things promised; they only saw them and welcomed them from a distance. And they admitted that they were aliens and strangers on earth. People who say such things show that they are looking for a country of their own. If they had been thinking of the country they had left, they would have had opportunity to return. Instead, they were longing for a better country—a heavenly one. Therefore God is not ashamed to be called their God, for he has prepared a city for them.
By faith Abraham, when God tested him, offered Isaac as a sacrifice. He who had received the promises was about to sacrifice his one and only son, even though God had said to him, "It is through Isaac that your offspring will be reckoned." Abraham reasoned that God could raise the dead, and figuratively speaking, he did receive Isaac back from death.
By faith Isaac blessed Jacob and Esau in regard to their future. By faith Jacob, when he was dying, blessed each of Joseph's sons, and worshiped as he leaned on the top of his staff.
By faith Joseph, when his end was near, spoke about the exodus of the Israelites from Egypt and gave instructions about his bones.
By faith Moses' parents hid him for three months after he was born, because they saw he was no ordinary child, and they were not afraid of the king's edict. By faith Moses, when he had grown up, refused to be known as the son of Pharaoh's daughter. He chose to be mistreated along with the people of God rather than to enjoy the pleasures of sin for a short time. He regarded disgrace for the sake of Christ as of greater value than the treasures of Egypt, because he was looking ahead to his reward. By faith he left Egypt, not fearing the king's anger; he persevered because he saw him who is invisible. By faith he kept the Passover and the sprinkling of blood, so that the destroyer of the firstborn would not touch the firstborn of Israel. By faith the people passed through the Red Sea as on dry land; but when the Egyptians tried to do so, they were drowned.
By faith the walls of Jericho fell, after the people had marched around them for seven days.
By faith the prostitute Rahab, because she welcomed the spies, was not killed with those who were disobedient.
And what more shall I say? I do not have time to tell about Gideon, Barak, Samson, Jephthah, David, Samuel and the prophets, who through faith conquered kingdoms, administered justice, and gained what was promised; who shut the mouths of lions, quenched the fury of the flames, and escaped the edge of the sword; whose weakness was turned to strength; and who became powerful in battle and routed foreign armies. Women received back their dead, raised to life again. Others were tortured and refused to be released, so that they might gain a better resurrection. Some faced jeers and flogging, while still others were chained and put in prison. They were stoned; they were sawed in two; they were put to death by the sword. They went about in sheepskins and goatskins, destitute, persecuted and mistreated—the world was not worthy of them. They wandered in deserts and mountains, and in caves and holes in the ground. These were all commended for their faith, yet none of them received what had been promised. God had planned something better for us so that only together with us would they be made perfect.”
Even Genesis says that Abraham was declared righteous (holy) by faith:
“Abram believed the LORD, and he credited it to him as righteousness.” (Gen. 15:6)
Modern evangelists have often used verses from the book of Romans to illustrate the way to salvation, in what they call “The Romans Road.” Typically, it usually goes something like this:
1. We must acknowledge God as the Creator of everything, accepting our humble position in God's created order and purpose.
"For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse, because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened."
2. We must realize that we are sinners and that we need forgiveness. None of us are worthy under God’s standards.
“For all have sinned, and fall short of the glory of God.”
3. God gave us the way to be forgiven of our sins. He showed us His love by giving us the potential for life through the death of His Son, Jesus Christ.
“But God demonstrates His love toward us, in that, while we were still sinners, Christ died for us.”
4. If we remain sinners, we will die. However, if we repent of our sins, and accept Jesus Christ as our Lord and Savior, we will have eternal life.
“For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.”
5. Confess that Jesus Christ is Lord and believe in your heart that God raised Him from the dead and you are saved.
“That if you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved. For with the heart one believes unto righteousness, and with the mouth confession is made unto salvation.”
6. There are no other religious formulas or rituals. Just call upon the name of the Lord and you will be saved!
“For whoever calls on the name of the LORD shall be saved.”
7. Determine in your heart to make Jesus Christ the Lord of your life today.
"For of Him and through Him and to Him are all things, to whom be glory forever. Amen."
And yet, I think that not many people realize that the Old Testament teaches the same basic principles:
No one does good; not even one:
“The LORD looks down from heaven on the sons of men to see if there are any who understand, any who seek God. All have turned aside, they have together become corrupt; there is no one who does good, not even one.” (Psalm 14:2-3)
We are sinful at birth:
“Surely I was sinful at birth, sinful from the time my mother conceived me.” (Psalm 51:5)
The heart is deceitful above all things (i.e., we are sinners):
“The heart is deceitful above all things and beyond cure. Who can understand it?” (Jeremiah 17:9)
Unclean lips (i.e., we are sinners in need of forgiveness):
"Woe to me!" I cried. "I am ruined! For I am a man of unclean lips, and I live among a people of unclean lips, and my eyes have seen the King, the LORD Almighty." (Isaiah 6:5)
In contrast to those who think they are “good,” the Bible says that even the best ‘good deeds’ we do (our “righteous acts”) are like filthy rags (in the original language, the term means a woman’s menstruating rags) compared to God’s holiness:
“All of us have become like one who is unclean, and all our righteous acts are like filthy rags; we all shrivel up like a leaf, and like the wind our sins sweep us away.” (Isaiah 64:6)
God will blot out sinners from His book:
“The LORD replied to Moses, "Whoever has sinned against me I will blot out of my book.” (Exodus 32:33)
There was no sacrifice for willful sins:
"But anyone who sins defiantly, whether native-born or alien, blasphemes the LORD, and that person must be cut off from his people. Because he has despised the LORD's word and broken his commands, that person must surely be cut off; his guilt remains on him." (Numbers 15:30-31)
Prayer to blot out our iniquity (sin):
“Hide your face from my sins and blot out all my iniquity.” (Psalm 51:9)
King David cried out to God for mercy:
“Have mercy on me, O God, according to your unfailing love; according to your great compassion blot out my transgressions.” (Psalm 51:1 [and the rest of Psalm 51])
Isaiah, the Old Testament prophet, was saved by God’s mercy:
“With it he touched my mouth and said, "See, this has touched your lips; your guilt is taken away and your sin atoned for." (Isaiah 6:7)
Sins were forgiven by a blood sacrifice:
“For the life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar; it is the blood that makes atonement for one's life.” (Leviticus 17:11)
Jews no longer practice animal sacrifice, and Christians never practiced animal sacrifice. In fact, the first Jewish temple (where sacrifices were performed) was destroyed for 70 years because of Israel’s disobedience, and the second temple was destroyed about 40 years after Jesus’ death (this also means that the Jewish genealogies have been lost, so that no one can claim that their lineage goes back to King David, and therefore cannot rightfully claim that they are the Messiah…the only Jewish genealogy we have left today is that of Jesus; we have both His maternal and His paternal genealogy; and His lineage DOES go back to King David, which is one requirement of the promised Messiah).
Christ Jesus’ death on the cross was the final, ultimate sacrifice for sins. For all who are believers, Christ Jesus is the ultimate and perfect High Priest. No other sacrifice for sins is needed, for Jesus has fulfilled all of that in Himself.