Musar zu Bereschit 12:7

Concerning the interval of a year until such shoots take root, or, allegorically, until Abraham's physical transplantation to the land of Canaan is reflected in his entry into the ארץ ישראל העליון, the celestial counterpart of the land of Israel, the Torah goes on to say in 12,6: וירא ה' אל אברם ויאמר לזרעך אתן את הארץ הזאת, ויבן שם מזבח לה' הנראה אליו. "G–d appeared to Abram saying: To your descendants I shall give this land. He (Abram) built an altar there for the G–d who had appeared to him." Why does the Torah in this instance preface G–d's appearance with the words וירא ה' ויאמר, something that we do not find in 12,1?