Faith is the human hand of the arm stretched out to receive from God's hand the gift that He has given us, i.e justification. Faith IN the One who justifies the ungodly, and in HIS work, will save us. If we do not believe, we are calling God a liar - which is the thing that condemns:
Christ paid the price, according to the scripture. The blood of Christ and the empty tomb proves it. Nothing we can do, nothing other than the blood of Christ and the empty tomb will ever prove that we belong to Him and that we are saved, if we believe. There is nothing more that we can add to it, because Christ died for us while we were sinners (Romans 5:8), and that is what saved us - Christ's death, and Christ's resurrection.
"For whatsoever is born of God overcomes the world: and this is the victory that overcomes the world, even our faith. Who is he that overcomes the world, but he that believes that Jesus is the Son of God?" -- John 5:4-5.
WHAT HUMAN EFFORT CANNOT DO
"Abide in me, and I in you. As the branch CANNOT BEAR FRUIT OF ITSELF, except it abide in the vine; no more can all of you, except all of you abide in me. I am the vine, all of you are the branches: He that abides in me, and I in him, the same brings forth much fruit: for without me all of you can do nothing. If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned." -- John 15:4-6.
|| But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, willful restrain: against such there is no law. || -- Galatians 5:22-23.
|| Owe no man any thing, but to love one another: for he that loves another has fulfilled the law. For this, Thou shalt not commit adultery, Thou shalt not kill, Thou shalt not steal, Thou shalt not bear false witness, Thou shalt not covet; and if there be any other commandment, it is briefly comprehended in this saying, namely, Thou shalt love thy neighbour as thyself.
Love works no ill to his neighbour: therefore love is the fulfilling of the law. || -- Romans 13:8-10.
Good works that are produced through faith in Christ alone are the fruit of the Spirit, the fruit of the Vine. Salvation is all of Christ, from start to finish (Philippians 1:6) and faith in Christ alone (John 3:18; 1 John 5:4-5) does not include faith in our own human effort.
Good works flow from faith in Christ and in His Word. Not the other way around. Our salvation and our justification does not depend upon us, but on Jesus the Messiah and upon His faithfulness to His Word and through our faith in His Word, because God's Word is truth.
To believe that it costs the believer something "to prove that we're saved" is adding human effort to Christ's finished work, and the one who does this is proving nothing except His lack of belief (faith) in the Word of God and the finished work of Christ.
The New Testament is teaching us that God has saved us. He has justified us by Christ's blood. Like in the case of Abraham, those who believe God are credited with Christ's righteousness. They are justified through their faith.
WHAT HUMAN EFFORT CAN DO
Peter wrote that God has "bestowed upon those who believe in Jesus precious and magnificent promises, so that by means of what was promised we may become partakers of the divine nature, after escaping the worldly corruption that is produced by evil desire."
Then he added:
2 Peter 1:4-8:
-- "For this very reason, make every effort to ADD to your faith:
Excellence, to excellence, knowledge; to knowledge, self-control; to self-control, perseverance; to perseverance, godliness; to godliness, brotherly affection; to brotherly affection, unselfish love."
Why add this?
"Because if these things are really yours and are continually increasing, they will keep you from becoming ineffective and unproductive in your pursuit of knowing our Lord Jesus Christ more intimately." -- 2 Peter 1:4-8
We cannot add our salvation or our justification through human effort, because it was all accomplished by Christ, but now, knowing that we are saved by Christ and justified by Christ through our faith (and not by human effort), for our own sake we should nevertheless make an effort to be diligent to add to our faith in Christ the list of things Peter mentioned above,
and we are doing so in order that we will kept from becoming ineffective and unproductive in our pursuit of knowing our Lord Jesus Christ more intimately.
Nevertheless when we bear fruit unto God we are not justified by our faith or by our works. We are justified through our faith IN Him and in the blood and resurrection which justified us - HIS blood and resurrection.