Saying, Surely blessing I will bless thee, and multiplying I will multiply thee. Saying, Surely blessing I will bless thee - I will continue to bless thee.
Multiplying I will multiply thee - I will continue to increase thy posterity. In the most literal manner God continues to fulfill this promise; genuine Christians are Abraham's seed, and God is increasing their number daily. See the notes on Genesis 22:12-18 (note); and Genesis 23:1 (note).