Chasidut for Kiddushin 163:1

Our sages in Yuma 28 express this thought when they ‎said that Avraham kept all the commandments of the Torah ‎down to the minutest detail such as ‎ערובי תבשילין‎, a rabbinic ‎ordinance enabling us to cook and bake on the festival in ‎preparation for the Sabbath on the next day, something ‎ordinarily forbidden as it appears as if one used a holy day to ‎prepare for the mundane day following, by having made ‎appropriate preparation for the observance of this very festival ‎on the eve of the festival in question by having prepared basic ‎meals for it. To the question how one could “fulfill” ‎commandments of the Torah at a time when the Torah had not ‎been revealed yet, the answer is that when man endeavours ‎through intense mental concentration to divine what is pleasing ‎to his Creator, he can tune in to the appropriate “wavelength.” ‎Avraham was the first individual who succeeded in doing this. ‎Avraham had succeed in placing all his 248 limbs at G’d’s disposal, ‎so that he was inspired with divining the will of his ‎Creator.
[Once the Torah had been given this feat could not be ‎repeated, just as the akeydah, Avraham’s offering his son as ‎a sacrifice to G’d in response to G’d’s request, could not ever be ‎repeated. Ed.]‎
According to tradition each of our limbs has a ‎function to perform for the 248 positive commandments of the ‎Torah. In fact, unless these limbs were used to perform G’d’s ‎commandments, they have no claim to life on this earth (or at ‎least in the Land of Israel). In a descending order, the head fulfils ‎the commandment of wearing tefillin. As long as Avram did ‎not live in the Holy Land, he had not had an opportunity to fulfill ‎any of these ‎מצות‎, “as yet unrevealed commandments,” as there ‎would be many commandments that could not be fulfilled even ‎after the Torah had been given, since they are not inextricably ‎tied to the soil of Land of Israel. He was therefore “missing” a ‎considerable number of limbs in his body, limbs that could not ‎perform their real tasks until he had settled in the Holy ‎Land.
Avraham was aware of this; this is why he had served ‎the Lord by the first method that we described earlier, i.e. by ‎selfless devotion to G’d, negating any claim to the comforts life on ‎this earth affords the creature living it, serving Him exclusively ‎from the ‎אין‎ aspect of the universe. This helps explain why he ‎allowed himself to be thrown into a fiery furnace by Nimrod in ‎order to demonstrate his utter devotion to the Creator. Once he ‎moved to the Holy Land, there was no more need for him to ‎demonstrate his loyalty to G’d by such negation of his entire ‎body.
If the reader were to ask that Yitzchok’s being offered as ‎a potential sacrifice to G’d occurred in the Holy Land, something ‎that does not appear to conform to the principle just described, ‎the answer is quite simple. Yitzchok’s being offered as a sacrifice ‎was the fulfillment of an express command by G’d, whereas G’d ‎had never told Avram to put his life on the line in his theological ‎confrontation with Nimrod. [In fact some commentators, ‎especially Rabbi Yitzchak Arama in his Akeydat Yitzchok, are ‎extremely critical of Avraham for having done what he did ‎without express permission from G’d. Ed.]
Since Avraham’s ‎service to the Lord was based on his attachment to the ‎אין‎, the ‎purely metaphysical domains of the universe, it is clear that he ‎could not draw down some of G’d’s largesse to the earth, the ‎domain of the ‎יש‎, the primarily physical, material domain of the ‎universe.