הִשָּׁמְר֣וּ לָכֶ֗ם פֶּֽן־תִּשְׁכְּחוּ֙ אֶת־בְּרִ֤ית יְהוָה֙ אֱלֹ֣הֵיכֶ֔ם אֲשֶׁ֥ר כָּרַ֖ת עִמָּכֶ֑ם וַעֲשִׂיתֶ֨ם לָכֶ֥ם פֶּ֙סֶל֙ תְּמ֣וּנַת כֹּ֔ל אֲשֶׁ֥ר צִוְּךָ֖ יְהוָ֥ה אֱלֹהֶֽיךָ׃
Take heed unto yourselves, lest ye forget the covenant of the LORD your God, which He made with you, and make you a graven image, even the likeness of any thing which the LORD thy God hath forbidden thee.
Tur HaArokh
השמרו לכם, “Take care of your selves!” Even though I am not crossing the river with you, I am exhorting you to be most careful.
Mizrachi
He added, "things," as the word, "all," is always attached to another word. And see that before it was written (4:16), "the likeness of all symbols."