The promise to Abraham that was passed through Jacob (Israel) was that through the single seed would all the nations be blessed. That single seed is Christ Jesus.
The preceding verse speaks to the rejection of genetic Israel while this verse speaks to spiritual Israel - the BodyOfChrist composed of -> every believer InChrist Jesus who is -> filled with His HolySpirit.
It is in becoming SonsOfTheHolySpirit that we are one with our Creator.