The just shall live by faith.
This phrase is used 4 times in Scripture:
Habbakuk 2:4
Romans 1:17
Galatians 3:11
Hebrews 10:38
Habakkuk 2:1-4 I will stand upon my watch, and set me upon the tower, and will watch to see what he will say unto me, and what I shall answer when I am reproved. And the LORD answered me, and said, Write the vision, and make it plain upon tables, that he may run that readeth it. For the vision is yet for an appointed time, but at the end it shall speak, and not lie: though it tarry, wait for it; because it will surely come, it will not tarry. Behold, his soul which is lifted up is not upright in him: but the just shall live by his faith.
Habakkuk set himself to watch. He waited to see what would be spoken to him after he cried to the Lord as shown in chapter 1. His concern was that salvation was being withheld; he cried unto the Lord and asked how long shall I cry, and thou wilt not hear! even cry out unto thee of violence, and thou wilt not save! (Hab 1:2).
The Lord answered and told Habakkuk He would work a work ... which ye will not believe, though it be told you (Hab 1:5). The Lord told Habakkuk He would raise up the Chaldeans and they were terrible and dreadful (Hab 1:7), they shall come all for violence (Hab 1:9).
Habakkuk replied in Hab 1:12-17 and then in Hab 2:1, Habakkuk set himself to hear from the Lord.
And the Lord answered him and told him the vision is yet for an appointed time, but at the end it shall speak, and not lie: though it tarry, wait for it; because it will surely come, it will not tarry (Hab 2:3). The "it" in this verse is really a "He" and the "He" is the Lord Jesus Christ. That is what Habakkuk and all the prophets and people before and after Habakkuk were waiting for --- Messiah.
Behold, his soul which is lifted up is not upright in him: but the just shall live by his faith (Hab 2:4).
This verse describes two types of people:
those who are not upright and who reject Messiah;
and those who live by faith in Messiah.
Romans 1:16-17 For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek. For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
The righteousness of God is revealed from faith to faith. It is faith which brings us to righteousness and it is faith which continues to keep us justified before God.
It is not that works bring us to faith and then we're justified.
Nor is it faith that brings us to righteousness and then works which justifies us.
It is faith which justifies, and our justification is sustained by faith.
Galatians 3:10-11 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. But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith.
Even if we were to continue in all things written in the book of the law and we were able to keep the law perfectly, our keeping the law would not result in our being justified. Our justification rests entirely in faith, not in the works of the law.
Hebrews 10:35-39 Cast not away therefore your confidence, which hath great recompence of reward. For ye have need of patience, that, after ye have done the will of God, ye might receive the promise. For yet a little while, and he that shall come will come, and will not tarry. Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him. But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul.
We live by faith in God's promises and we patiently wait for ultimate fulfillment of those promises.
To draw back would exhibit a lack of faith.
To patiently endure without wavering exhibits complete trust and faith in God Who has promised that our Lord and Savior will come, and will not tarry.
Therefore, we wait yet a little while even if that little while comes after our life on this earth has come to its end. We do the will of God and we surely shall receive the promise.
We, in our day and time, are in the same situation as Habakkuk. While he waited for the first coming of Messiah, we await the return of Messiah. If we continue reading in Hebrews, we get to chapter 11 and read of those who by faith lived their lives and obtained a good report through faith (Heb 11:39). We are then assured God provided some better thing for us (Heb 11:40) and that better thing for us is shown to be Jesus the author (beginning) and finisher (end) of our faith (Heb 12:2) and we are to consider Him that endured such contradiction of sinners against Himself, lest ye be wearied and faint in your minds (Heb 12:3).
So the encouragement is that we begin in faith (Rom 1:17), we continue in faith (Gal 3:11), and we finish in faith (Heb 10:38).