לָכֵ֕ן כֹּ֥ה אֶעֱשֶׂה־לְּךָ֖ יִשְׂרָאֵ֑ל עֵ֚קֶב כִּֽי־זֹ֣את אֶֽעֱשֶׂה־לָּ֔ךְ הִכּ֥וֹן לִקְרַאת־אֱלֹהֶ֖יךָ יִשְׂרָאֵֽל׃
Therefore thus will I do unto thee, O Israel; Because I will do this unto thee, Prepare to meet thy God, O Israel.
Rashi on Amos
because—Since you hear from the mouth of My prophets that I will do this to you.