פּירוש אויף בראשית 15:8

?ויאמר.. במה אדע כי אירשנה, he meant: “how do I know that my son will inherit it?” We have a similar construction in Genesis 48,22 אשר לקחתי מיד האמורי, where Yaakov also does not mean that he, personally, had battled the Emorite, but that his sons had done so successfully. The meaning of the words במה אדע cannot be that the same man who had just been given credit for his utter faith in G’d now has developed doubts, nothing having occurred to cause such doubts. He wanted to know how he could be certain that when his sons, i.e. offspring, would inherit the land that it would remain theirs forever. Perhaps, due to some sin, future generations might forfeit their claim to the land of Canaan, just as the present occupants had forfeited their claim through their sins. Unless they had, why would G’d want to dispossess them? He hoped that just as G’d had shown him the stars as an illustration that his offspring would be people of great substance, so G’d would show him a further illustration of a means by which his offspring would reinforce their title to that land once they had settled in it.

במה אדע, for possibly my descendants will sin and forfeit their claim to this land.

במה אדע כי אירשנה, “how will I know that I will inherit it?” Avram meant: “by means of which merit will I inherit it?” G’d answered: “by means of the merit of the sacrifices you are about to offer.” This is the meaning of the verse קחה לי “take for Me” (verse 9). When G’d said this He again appeared to Avram as the attribute of א-דני, but in this instance it was followed by the letter ה [the name “Hashem” with the vowels of the name “elohim.”] to show that the attribute of Mercy was also involved to some extent.
This amounts to the name שדי. You know that we must not pronounce the Ineffable Name as it is spelled. Hence the sages in charge of vocalisation adjusted the vowels in a manner that make them suitable for reading. We must use either the form “elohim,” or the form “adonai,” when pronouncing G’d’s name. A scriptural reminder that this is so is found in Chabakuk 2,2 וה' בהיכל קדשו הס מפניו כל הארץ, “and the Lord is in the Sanctuary of His Holiness; silence in His presence everyone on earth!” This verse is a reminder that only inside the Holy of Holies may the Ineffable Name be pronounced as we would read it had we not been cautioned not to read it as it is spelled.