(1) The LORD appeared to him by the plains of Mamre; he was sitting at the entrance of the tent as the day grew hot.
פתח האהל. לִרְאוֹת אִם יֵשׁ עוֹבֵר וָשָׁב וְיַכְנִיסֵם בְּבֵיתוֹ:
At the tent door. That he might see whether anyone passed by, and invite him into the house.
(20) You will keep faith with Jacob, Loyalty to Abraham, as You promised on oath to our fathers in days gone by.
Rabbi Samlai taught: With regard to the Torah, its beginning is an act of kindness and its end is an act of kindness. Its beginning is an act of kindness, as it is written: “And the Lord God made for Adam and for his wife garments of skin, and clothed them” (Bereishis 3:21). And its end is an act of kindness, as it is written: “And he was buried in the valley in the land of Moav” (Deuteronomy 34:6).
ואמר רבי אמי בר אבא בן שלוש שנים הכיר אברהם את בוראו שנאמר עקב אשר שמע אברהם בקולי (בראשית כו, ה) חושבניה מאה ושבעין ותרין
And Rabbi Ami bar Abba said: Abraham recognized his Creator at the age of three years, as it is stated: “Because [ekev] Abraham hearkened to My voice” (Bereishis 26:5). The numerical value of the letters of the word ekev is 172, indicating that he observed the halakha for this many years. If Abraham lived until 175 then his first recognition of the Creator must have been at the age of three.
ואמר רבי חמא ברבי חנינא מאי דכתיב (דברים יג, ה) אחרי ה' אלהיכם תלכו...להלך אחר מדותיו
And Rabbi Chama bar Chanina said: What is the meaning of that which is written: (Devarim 13:5) "Follow none but the LORD your God"... that one should follow His attributes.