וַיֹּ֤אמֶר שְׁמוּאֵל֙ אֶל־שָׁא֔וּל אֹתִ֨י שָׁלַ֤ח יְהוָה֙ לִמְשָׁחֳךָ֣ לְמֶ֔לֶךְ עַל־עַמּ֖וֹ עַל־יִשְׂרָאֵ֑ל וְעַתָּ֣ה שְׁמַ֔ע לְק֖וֹל דִּבְרֵ֥י יְהוָֽה׃ (ס)
און שמואל האָט געזאָגט צו שָאולן: מיך האָט גאָט געשיקט דיך צו זאַלבן פֿאַר אַ מלך איבער זײַן פֿאָלק איבער ישׂראל; דרום הער אַצונד צו דעם קָול פֿון די װערטער פֿון גאָט.
Rashi
Now obey Adonoy's words. Once you acted foolishly,1 Shaul had acted improperly by not waiting for Shmuel [Above 13:8-14] as he had been instructed, therefore, Shmuel is warning him now to be careful. but now be careful [in your actions].
Tze'enah Ure'enah
“Samuel said to Saul” [15:1]. Samuel said to King Saul: the Holy One has sent me to make you a king over Israel. Therefore, it is just that you must listen to God’s commands that you should take revenge against Amalek.1Radak, I Samuel, 15:1.