Another interpretation: why did they so cherish circumcision? Because they knew that it was destined to save their children from Gehinnom, as it is said, "Therefore Sheol has enlarged her appetite and opened her mouth without measure [li-vli choq]" (Isaiah 5:14) - and choq means nothing other than circumcision, as it is said, "which He made with Abraham, and His oath to Isaac, and confirmed it to Jacob for a statute [le-choq]" (Psalms 105:9-10). And Israel, who were circumcised, escape from it, as it is said, "When you pass through the waters I will be with you... when you walk through the fire you shall not be burned" (Isaiah 43:2).
Why the Patriarchs Cherished Circumcision as Rescue From Gehinnom
Yalkut Shimoni on Torah 106:6
דָּבָר אַחֵר, לָמָּה הָיוּ מְחַבְּבִין אֶת הַמִּילָה, שֶׁהָיוּ יוֹדְעִין שֶׁהִיא עֲתִידָה לְהַצִּיל אֶת בְּנֵיהֶם מִגֵּיהִנֹם, שֶׁנֶּאֱמַר "לָכֵן הִרְחִיבָה שְׁאוֹל נַפְשָׁהּ וּפָעֲרָה פִּיהָ לִבְלִי חֹק" וְאֵין חֹק אֶלָּא מִילָה, שֶׁנֶּאֱמַר (תהלים קה, ט י) "אֲשֶׁר כָּרַת אֶת אַבְרָהָם וּשְׁבוּעָתוֹ לְיִשְׂחָק וַיַּעֲמִידֶהָ לְיַעֲקֹב לְחֹק". וְיִשְׂרָאֵל שֶׁהָיוּ מוּלִין נִמְלָטִין מִמֶּנָּה, שֶׁנֶּאֱמַר (ישעיה מג, ב) "כִּי תַעֲבֹר בַּמַּיִם אִתְּךָ אָנִי וְגוֹ' כִּי תֵלֵךְ בְּמוֹ אֵשׁ לֹא תִכָּוֶּה".