(א) וַיֵּרָ֤א אֵלָיו֙ ה' בְּאֵלֹנֵ֖י מַמְרֵ֑א וְה֛וּא יֹשֵׁ֥ב פֶּֽתַח־הָאֹ֖הֶל כְּחֹ֥ם הַיּֽוֹם׃ (ב) וַיִּשָּׂ֤א עֵינָיו֙ וַיַּ֔רְא וְהִנֵּה֙ שְׁלֹשָׁ֣ה אֲנָשִׁ֔ים נִצָּבִ֖ים עָלָ֑יו וַיַּ֗רְא וַיָּ֤רׇץ לִקְרָאתָם֙ מִפֶּ֣תַח הָאֹ֔הֶל וַיִּשְׁתַּ֖חוּ אָֽרְצָה׃ (ג) וַיֹּאמַ֑ר אדושם אִם־נָ֨א מָצָ֤אתִי חֵן֙ בְּעֵינֶ֔יךָ אַל־נָ֥א תַעֲבֹ֖ר מֵעַ֥ל עַבְדֶּֽךָ׃ (ד) יֻקַּֽח־נָ֣א מְעַט־מַ֔יִם וְרַחֲצ֖וּ רַגְלֵיכֶ֑ם וְהִֽשָּׁעֲנ֖וּ תַּ֥חַת הָעֵֽץ׃ (ה) וְאֶקְחָ֨ה פַת־לֶ֜חֶם וְסַעֲד֤וּ לִבְּכֶם֙ אַחַ֣ר תַּעֲבֹ֔רוּ כִּֽי־עַל־כֵּ֥ן עֲבַרְתֶּ֖ם עַֽל־עַבְדְּכֶ֑ם וַיֹּ֣אמְר֔וּ כֵּ֥ן תַּעֲשֶׂ֖ה כַּאֲשֶׁ֥ר דִּבַּֽרְתָּ׃ (ו) וַיְמַהֵ֧ר אַבְרָהָ֛ם הָאֹ֖הֱלָה אֶל־שָׂרָ֑ה וַיֹּ֗אמֶר מַהֲרִ֞י שְׁלֹ֤שׁ סְאִים֙ קֶ֣מַח סֹ֔לֶת ל֖וּשִׁי וַעֲשִׂ֥י עֻגֽוֹת׃ (ז) וְאֶל־הַבָּקָ֖ר רָ֣ץ אַבְרָהָ֑ם וַיִּקַּ֨ח בֶּן־בָּקָ֜ר רַ֤ךְ וָטוֹב֙ וַיִּתֵּ֣ן אֶל־הַנַּ֔עַר וַיְמַהֵ֖ר לַעֲשׂ֥וֹת אֹתֽוֹ׃ (ח) וַיִּקַּ֨ח חֶמְאָ֜ה וְחָלָ֗ב וּבֶן־הַבָּקָר֙ אֲשֶׁ֣ר עָשָׂ֔ה וַיִּתֵּ֖ן לִפְנֵיהֶ֑ם וְהֽוּא־עֹמֵ֧ד עֲלֵיהֶ֛ם תַּ֥חַת הָעֵ֖ץ וַיֹּאכֵֽלוּ׃
(1) ה' appeared to him by the terebinths of Mamre; he was sitting at the entrance of the tent as the day grew hot. (2) Looking up, he saw three figures standing near him. Perceiving this, he ran from the entrance of the tent to greet them and, bowing to the ground, (3) he said, “My lords! If it please you, do not go on past your servant. (4) Let a little water be brought; bathe your feet and recline under the tree. (5) And let me fetch a morsel of bread that you may refresh yourselves; then go on—seeing that you have come your servant’s way.” They replied, “Do as you have said.” (6) Abraham hastened into the tent to Sarah, and said, “Quick, three seahs of choice flour! Knead and make cakes!” (7) Then Abraham ran to the herd, took a calf, tender and choice, and gave it to a servant-boy, who hastened to prepare it. (8) He took curds and milk and the calf that had been prepared and set these before them; and he waited on them under the tree as they ate.
Tosafot teaches us that there is a Midrash which says that Avraham followed all Thora laws and also the “fences” surrounding them to protect us against violating the prohibition itself. (Which means that he also observed the additional laws which protect us from overstepping the Mitzwot)
So why does it say "He took curds and milk and the calf that had been prepared and set these before them"
Some Psukim before it is stated: "(7) Then Abraham ran to the herd, took a calf, tender and choice, and gave it to a servant-boy, who hastened to prepare it." and as we know meat needs time to get kosher, so Tosafot teaches that Avraham served the dairy products first and when the meat was ready he served the meat.
From this we can learn that it is important to look at all of the aspects of the Mitzwot and to fulfill even the smallest part of the Law.