Albert Barnes Commentary Hebrews 6:14

"saying, Surely blessing I will bless thee, and multiplying I will multiply thee." — Hebrews 6:14 (ASV)

Saying, Surely blessing I will bless thee. That is, I will certainly bless you. The phrase is a Hebrew mode of expression, used to denote emphasis or certainty—indicated by the repetition of a word. (Exodus 8:10; Joel 3:14; Judges 5:30; Judges 15:16).

Multiplying I will multiply thee. I will greatly increase you—I will grant you an exceedingly numerous posterity.