Why does the Posuk seem to imply that Avraham named his son before the bris? First:
וַיִּקְרָא אַבְרָהָם אֶת שֶׁם בְּנוֹ הַנּוֹלַד לוֹ אֲשֶׁר יָלְדָה לּוֹ שָׂרָה יִצְחָק
So he called his name Yitzchak, and then the next Posuk says:
וַיָּמָל אַבְרָהָם אֶת יִצְחָק בְּנוֹ בֶּן שְׁמֹנַת יָמִים כַּאֲשֶׁר צִוָּה אֹתוֹ אֱ־לֹהִים
and then they did the Bris (circumcision). Why is our Minhag to do the Bris and then name the child?