This entire set of verses needs to be addressed:
Galatians 3:5
He therefore that ministereth to you the Spirit, and worketh miracles among you, doeth he it by the works of the law, or by the hearing of faith?
3:6
Even as Abraham believed God, and it was accounted to him for righteousness.
3:7
Know ye therefore that they which are of faith, the same are the children of Abraham.
3:8
And the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.
3:9
So then they which be of faith are blessed with faithful Abraham.
3:10
For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in all things which are written in the book of the law to do them.
3:11
But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith.
3:12
And the law is not of faith: but, The man that doeth them shall live in them.
Justification can only be obtained through the blood of Jesus Christ.
Does this mean that every man on earth is now justified? No it does not. It means that the absolute bondage of sin unto death(hell) no longer has absolute hold on every man.
We are now able to be justified by His blood. How will man be justified by His blood? Only by the choosing of the Father (John 6:44).
How do we respond to the urging of the Father? By faith alone. How do we get faith? God made sure you heard the gospel by human instrumentation and that gospel came by way of the Word of God.(Romans 10:17).
We are without excuse.
Has everyone heard the Word of God? According to Romans 10:18,19 they have.
10:18
But I say, Have they not heard? Yes verily, their sound went into all the earth, and their words unto the ends of the world.
10:19
But I say, Did not Israel know? First Moses saith, I will provoke you to jealousy by them that are no people, and by a foolish nation I will anger you.
The Gospel of Jesus Christ has been presented to the entire earth in whom God imparted, Jews and Gentiles alike.
So where is our Justification? In Jesus Christ alone. It has nothing to do with us.
SO, you ask,
Do you think that in order to be justified -- declared righteous -- a sinner must do or think something?
I think the answer is that in order to be justified, a sinner who is chosen by God cannot help but think and do something. The ordered process is not understood by the question you asked.
Psalm 37:23
The steps of a good man are ordered by the LORD: and he delighteth in his way.
37:24
Though he fall, he shall not be utterly cast down: for the LORD upholdeth him with his hand.
37:25
I have been young, and now am old; yet have I not seen the righteous forsaken, nor his seed begging bread.
Love in Christ,
Jim