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).
Notes on the Whole Bible
Saying, Surely blessing I will bless thee - That is, I will certainly bless thee. The phrase is a Hebrew mode of expression, to denote emphasis or certainty - indicated by the repetition of a word; compare Genesis 14:23; Exodus 8:10; Joel 3:14; Judges 5:30; Judges 15:16.
Multiplying I will multiply thee - I will greatly increase thee - I will grant thee an exceedingly numerous posterity.
Concise Bible Commentary
The hope here meant, is a sure looking for good things promised, through those promises, with love, desire, and valuing of them. Hope has its degrees, as faith also. The promise of blessedness God has made to believers, is from God's eternal purpose, settled between the eternal Father, Son, and Spirit. These promises of God may safely be depended upon; for here we have two things which cannot change, the counsel and the oath of God, in which it is not possible for God to lie; it would be contrary to his nature as well as to his will. And as He cannot lie; the destruction of the unbeliever, and the salvation of the believer, are alike certain. Here observe, those to whom God has given full security of happiness, have a title to the promises by inheritance. The consolations of God are strong enough to support his people under their heaviest trials. Here is a refuge for all sinners who flee to the mercy of God, through the redemption of Christ, according to the covenant of grace, laying aside all other confidences. We are in this world as a ship at sea, tossed up and down, and in danger of being cast away. We need an anchor to keep us sure and steady. Gospel hope is our anchor in the storms of this world. It is sure and stedfast, or it could not keep us so. The free grace of God, the merits and mediation of Christ, and the powerful influences of his Spirit, are the grounds of this hope, and so it is a stedfast hope. Christ is the object and ground of the believer's hope. Let us therefore set our affections on things above, and wait patiently for his appearance, when we shall certainly appear with him in glory.