Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of his counsel, confirmed it by an oath: The heirs of promise - All the believing posterity of Abraham, and the nations of the earth or Gentiles in general.
The immutability of his counsel - His unchangeable purpose, to call the Gentiles to salvation by Jesus Christ; to justify every penitent by faith; to accept faith in Christ for justification in place of personal righteousness; and finally to bring every persevering believer, whether Jew or Gentile, to eternal glory.