וַיֹּ֨אמֶר יְהוָ֜ה אֶל־שְׁמוּאֵ֗ל אַל־תַּבֵּ֧ט אֶל־מַרְאֵ֛הוּ וְאֶל־גְּבֹ֥הַּ קוֹמָת֖וֹ כִּ֣י מְאַסְתִּ֑יהוּ כִּ֣י ׀ לֹ֗א אֲשֶׁ֤ר יִרְאֶה֙ הָאָדָ֔ם כִּ֤י הָֽאָדָם֙ יִרְאֶ֣ה לַעֵינַ֔יִם וַיהוָ֖ה יִרְאֶ֥ה לַלֵּבָֽב׃
האָט גאָט געזאָגט צו שמואלן: זאָלסט ניט קוקן אױף זײַן אױסזען, און אױף זײַן הױכן װוּקס, װאָרום איך װיל אים ניט; װאָרום עס איז ניט װי דער מענטש זעט; װײַל דער מענטש זעט נאָכן אָנבליק, אָבער גאָט זעט נאָכן האַרצן.
Rashi
For I have rejected him. Because he is a quick tempered person, as it is stated, 'And Eliov became angry with Dovid.'4 Below 17:28. Also, see Maseches Pesachim 66b, that Eliov actually possessed the qualities of a king but ‘ה rejected him because he had a bad temper.
Rashi
For it is not as man perceives it. Even though you called yourself a seer, when you said to Shaul, 'I am the seer,'5Above 9:19. ה׳ punished Shmuel for inferring albeit an infinitesimal of pride by saying “I am the seer.” Moshe was similarly punished for saying “the matter that will be too difficult for you, present to me and I will hear it.” [Devarim 1:17]—Sifre, Devarim 1:17 here I am informing you that you do not see.