To be an obstacle in someone's way
It turned into a stumbling block for him. Something not harmful at first that turns over time into an obstacle on the way. It turned into a snare for him (mokeish literally means snare).
("They shall not dwell in your land, lest they make you sin against me, because you shall serve their God, for it shall be a snare unto you" - Shemot 23:33, the Lord to the people of Israel concerning the inhabitants of the land)
Translation
Expression (Hebrew)
הָיָה לוֹ לְמוֹקֵשׁ, הָיָה לְמוֹקֵשׁ
Definition (Hebrew)
נֶהְפַּךְ לוֹ לְמִכְשׁוֹל. דָּבָר לֹא מַזִּיק לִכְאוֹרָה שֶׁנֶּהְפַּךְ בַּהֶמְשֵׁךְ לְמִכְשׁוֹל בַּדֶּרֶךְ. נֶהְפָּךְ לוֹ לְמַלְכֹּדֶת (מוֹקֵשׁ מַשְׁמָע מַלְכֹּדֶת).
("לֹא יֵשְׁבוּ בְּאַרְצְךָ פֶּן יַחֲטִיאוּ אֹתְךָ לִי כִּי תַעֲבֹד אֶת אֱלֹהֵיהֶם, כִּי יִהְיֶה לְךָ לְמוֹקֵשׁ"- שְׁמוֹת כג לג, ה' לְעַם יִשְׂרָאֵל בְּנוֹגֵעַ לְיוֹשְׁבֵי הָאָרֶץ )