Because

Genesis 22:15-18

15 And the angel of the Lord called to Abraham a second time from heaven 16 and said, “By myself I have sworn, declares the Lord, because you have done this and have not withheld your son, your only son, 17 I will surely bless you, and I will surely multiply your offspring as the stars of heaven and as the sand that is on the seashore. And your offspring shall possess the gate of his enemies, 18 and in your offspring shall all the nations of the earth be blessed, because you have obeyed my voice. ” 

Jesus speaks to Abraham and to us. I will bless you because you have obeyed my voice. 

By His name He has sworn. By His name He saves. By His name He blesses.