We find the phrase “live by” a number of times in the Bible, explaining what gives us life.
BY THE WORD OF THE LORD
In Deuteronomy 8:3 we read:
“Man does not live by bread alone, but man lives by everything that proceeds out of the mouth of the LORD.”
In other words, “bread” gives life for our current life, but the word of the LORD is what really gives life. It is not immediately clear whether eternal life is intended.
BY OBEDIENCE TO THE LAW
The LORD said:
“You shall keep My statutes and My judgments, by which a man may live if he does them; I am the LORD” (Lev. 18:5).
This and other such statements are the basis of the Jewish view that one is justified by “the works of the Law” (Gal. 2:16). Paul quoted this verse to say that salvation, in the Old Testament, is through obedience to the Law:
“Moses writes that the man who practices the righteousness which is based on law shall live by that righteousness” (Rom. 10:5).
“The Law is not of faith; on the contrary, “he who practices them shall live by them.” (Gal. 3:12)
According to Ezekiel 33:12 and 19, “righteousness,” rather than “the works of the Law” brings life:
“A righteous man will not be able to live by his righteousness on the day when he commits sin”. …
“But when the wicked turns from his wickedness and practices justice and righteousness, he will live by them”.
It is also not clear whether Ezekiel meant eternal life.
Paul was very fond of Habakkuk 2:4, for it says that “faith” give life:
The soul of “the righteous”, who “live by his faith”, is “right within him.”
The following are some of Paul’s quotes from Habakkuk 2:4:
“No one is justified by the Law before God … for, “THE RIGHTEOUS MAN SHALL LIVE BY FAITH” (Gal. 3:11).
“The good news of the Christ … is the power of God to salvation to everyone who is believing” (YLT – Rom. 1:16).
“MY RIGHTEOUS ONE SHALL LIVE BY FAITH” (Hebr. 10:38).
In Romans 1:16, Paul interprets to “live” as “salvation.”