רמב"ן — ושב שם ועשה שם מזבח

Q — Hashem tells Yaakov 'קום עלה בית אל ושב שם ועשה שם מזבח'. The עליה and the מזבח are clear — but what is 'ושב שם'?

A — Ramban admits the difficulty ('לא ידעתי מהו ושב שם') and offers two readings. (1) Settle there first to undergo טהרה — either from the avoda zara just removed or from the corpse-tum'a of the killings at Shechem — before building the mizbeach, like Bnei Yisrael at Midian ('ואתם חנו מחוץ למחנה שבעת ימים'). (2) The deeper reading: 'לפנות מחשבתו לדבקה באל' — to prepare his mind for devekut before the avoda. (Sforno gives the same pshat, citing the chasidim ha'rishonim who would wait an hour before tefilla to focus their hearts.) The chiddush is that avodat ha'mizbeach requires not only physical purity but preparatory kavana — the work of building demands first the work of settling the mind.