A believer's justification is totally God's gift of grace. It is neither deserved nor merited, but it is given because God loved us.
John 3:16: For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
God gave His only begotten son so that we could have eternal life. This can be seen and understood vividly by a study of the words which are translated "freely".
One of the words for freely, dorean, literally means "without a cause". It can also be translated gratuitously, as a gift, out of favor, for no reason, unnecessarily. It is used in Romans 3:24 to show how God justified us.
Romans 3:24: Being justified freely by his grace through the redemption that is in Christ Jesus:
God justified us, acquitted us from guilt, without a cause. He did not have a reason for doing this other than His grace. There was nothing which we did to deserve the justification. We did not earn it. It was "out of favor", "as a gift". A gift is the antithesis of wages. Thus receiving the gift of justification and righteousness is "gratuitous", determined by God's goodness and love, not by our works, good or bad.
This is not so hard to understand when we look at Romans 5 and see how we received our sin nature.
Romans 5:12: Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:
Because of Adam's sin, we received the sin nature and death. Did we earn it? What did we do to deserve it? Only by being born did we have it come upon us.
Romans 5:15: But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many.
The free gift of God's grace is received the same way - not by any deserving or meriting. But it is greater because now we can reign in life by way of Jesus Christ and the righteousness which he made available to us.
Romans 5:17: For if by one man's offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ.)
In Christ Jesus we are justified without a cause, as a gift. In Christ Jesus we received redemption and righteousness. In Christ Jesus we can reign in life. This is salvation and wholeness and includes our life now as well as eternal life.
Romans 8:32: He that spared not his own Son, but delivered him up for us all, how shall he not with him also freely give us all things?
The word for "freely give" in this verse is charizomai. Its root is from charis, grace. Our justification was not based on works. So also our life continues on that basis. Our reigning in life now is by God's grace and continued giving to us as His sons.
Titus 3:5-7: Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost; Which he shed on us abundantly through Jesus Christ our Saviour; That being justified by his grace, we should be made heirs according to the hope of eternal life.
God saved us and poured His acceptance out on us abundantly. He declared that we were accepted in the beloved, in Christ Jesus. This pouring out of His grace is clear in the Aramaic translation of Ephesians 1:6.
Ephesians 1:6 (Aramaic Translation): that the glory of his grace would be glorified, which he has poured on us by way of his beloved [one],
So, from a brief look at the words for freely, the magnificence of God's grace can be realized even more. Without a cause, freely, as a gift, God poured out His love and justified us, gave us righteousness, eternal life. He continues to freely give so that we can reign in life now. This is not based upon any merit or deserving, but is all by His love.