the blessing of abraham

hey guys,
so i remember a lot of talk on here some time ago about the first call of abraham in Gen. 15, focusing on how God called abraham use His blessings to bless others. i think some of the stuff with reggie mcneal involved that passage, as well as some things i heard at the youth mission trip last summer with lance and ben.

in youth group, we've been going through the OT and how it all points to Jesus. in studying up on abraham, i noticed that Gal. 3 quotes Gen. 12, saying, "the Scripture, forseeing that God would justify the gentiles through faith, preached the Gospel beforehand to abraham, saying, 'in you shall all the nations be blessed.'"

my question is, if that is the God-authorized understanding of that verse, how do we interpret it as abraham as our example, to use what he has to bless others?