The word “Lord” in the Septuagint (Greek translation of the Old Testament) is the translation of the Hebrew name for God, which is Yahweh
(the almighty Creator who established a bond of love with people; in English translations in the Old Testament, it is commonly rendered as “Lord”). When Peter earlier used the word Lord
(e.g., 1 Peter 1:3) the term referred to Jesus Christ. So his now replacing the Septuagint's “Lord” with the term “God” makes unambiguous who it is that opposes the proud: God himself, as Proverbs 3:34 had also indicated.
5 Likewise, you who are younger, be subject to the elders. Clothe yourselves, all of you, with humility toward one another, for “God opposes the proud but gives grace to the humble.”