Habakkuk 2:4, "Behold, his soul is puffed up; it is not upright within him, but the righteous shall live by his faith."
The Lord is emphasizing that there are two kinds of people. The proud ("puffed up"), who are wicked and unjust ("not upright"), in contrast to the humble who are faithful and just (righteous"), before God. Pride looks to self while true faith looks outside of self unto God. The proud are not justified before the Lord and thus perish while the faithful and humble are justified thus are gifted salvation.
These Words of the Lord gave Habukkuk comfort while struggling with the Lord's use of the Babylonians to punish His people. That God had not abandoned them but rather was teaching His people the only way they could live an obedient righteous life and not perish like the prideful, selfish, and wicked do, was by focusing on things in heaven above and keeping a steadfast faith and love unto God their Creator, Savior and Lord.
Habukkuk 2:4 is such an important message from God that it is reemphasized in similar ways three times in the New Testament (Romans 1:17;Hebrews 10:38;Galatians 3:7).