Righteousness by Grace Vs. Righteousness by Deeds

A man in the Old Testament, could be righteous by his own deeds according to the law of God given through Moses. The law was the measuring rod of the righteousness of a person. Thus anybody who lived according to the law, was said to be righteous and could be worthy of being blessed by God.

When we consider Leviticus Chapter 26 and Deuteronomy Chapter 28, it is very clear that blessings of God for the Children of Israel were proportional to their obedience to follow the law or to keep the commandments in the law. As they were blessed when they obeyed the law, they were cursed when they disobeyed the law. Thus, their blessings depended on their performance.

Since the Children of Israel had to be righteous by keeping the law in order to be blessed, their righteousness was said to be the righteousness with the law.  By their deeds, they earned righteousness for God to bless them. This righteousness earned with the law could be considered as the price the Children of Israel had to pay for their blessings from God. God could continue to bless the Children of Israel for the price they paid by their righteousness with the law as the blessings they received were worthy of their price.

What are the blessings that could be purchased by the Children of Israel with their righteousness with the law?

The blessings proclaimed in Leviticus Chapter 26 & Deuteronomy Chapter 28 could be purchased by the Children of Israel with the righteousness earned by themselves by keeping the law. However, all of these blessings were material or earthly blessings.

THE MOST EXPENSIVE BLESSING

Apart from these earthly blessings, God wanted to offer the eternal salvation to man so that man could live forever in the kingdom of God. But the price of this salvation was so expensive that it could not be purchased with the righteousness of man that came to him with the law.

What is the price of this salvation?

The price of this salvation equals exactly the same  righteousness of God. In other words, for man to purchase this salvation, he had to be as righteous as God. 
For a man to be as righteous as God, there should not be a single sin in him. He should not know sin at all. Hence it was not possible for man to purchase his eternal salvation as every human is conceived with sin in his mother's womb since the day sin entered the first man, Adam. King David explains this nature of man in the below verse.

(Psalm 51:5)
Behold, I was shapen in iniquity; and in sin did my mother conceive me.

In the first place, man needed this salvation because of his sin. If man could come to a state where there would be no sin in him, he would not need a salvation. The Scripture says, "All have sinned and come short of the glory of God" (Romans 3:23).

But the good news was that right at the beginning, even before Adam lost his eternal life on earth, God had a plan for offering this salvation to man in case he would lose it. All Glory to God!

What was this plan?

The plan was to make God's only begotten son, Jesus Christ, who knew no sin and had God's righteousness in Him, a mere man and send to the world. When Jesus Christ became a man, he was the only man who knew no sin. Therefore, He became the only man who had the same righteousness of God.

According to God's plan, Jesus Christ as a man exchanged His righteousness which equaled God's righteousness with the sin in man by becoming sin so that man could receive God's righteousness without the law. Look at the below scripture.

(2Corinthians 5:21)
For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.

 In this exchange, the penalty of sin, which is death (Romans 6:23), had to be paid by Jesus Christ by sacrificing His human life on a cross.

(1Peter 2:24)
 Who his own self bare our sins in his own body on the tree, that we, being dead to sins, should live unto righteousness...

All who believe in Jesus Christ can exchange their sin with Jesus Christ for God's righteousness. Once this exchange is done, all could receive eternal salvation. 
 

Today, anyone who believes in Christ receives God's righteousness which is the cost of our salvation. As this cost was not born by us in order to receive our eternal salvation, we receive both righteousness and salvation by grace of God through our faith. Thus the righteousness that brings our salvation is called righteousness by grace through faith and the salvation which we receive by this righteousness is called salvation by grace through faith. 

(Romans 3:21-23)
But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets; Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference: For all have sinned, and come short of the glory of God;

RIGHTEOUSNESS BY DEEDS IN THE NEW TESTAMENT

Does God's righteousness in Christ, that has been transferred to us by grace though faith, replace our own righteousness that we should earn by our deeds?

In order to understand the answer to the above question, let's take an example... A very rich person buys you a luxurious vehicle, which you could never think of buying with your own money in your whole life.  This rich man bears the cost of this expensive vehicle just because you cannot afford to bear the cost. However, after the vehicle is gifted to you, the rich man expects you to maintain it with your own cost simply because you can afford to bear this cost.

Our eternal salvation is also just like this luxurious vehicle. God has bought it for us by sacrificing Jesus Christ, because we could not bear the cost. Now we have received this salvation as a gift from God. As you should maintain the vehicle with your cost, it is our responsibility to preserve this salvation with our righteousness by deeds. In other words, we have purchased our salvation with God's righteousness and preserve our salvation with our righteousness. Look at the below verse:

(Php 2:12)
Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling.

What does the phrase, "work out your salvation" in the above verse mean?

"Work out your own salvation" means "Preserve your own salvation with your righteousness". Thus, it is very clear that although our salvation is a gift from God, it is our responsibility to preserve it with our righteousness.

Hence, nobody becomes as righteous as God when the scripture says that God's righteousness is transferred to us through Christ. This righteousness is transferred in order that we become qualified by grace to receive our salvation. But God wants you and me to be righteous by our own deeds in order to preserve our salvation.