Verse 10: Then came the word of the LORD unto Samuel, saying…
Verse 11: (1 Sam. 15:35; Gen. 6:6, 7; 2 Sam. 24:16) It repenteth me that I have set up Saul to be king: for he is (Josh. 22:16; 1 Kings 9:6) turned back from following me, (1 Sam. 13:13; 15:3, 9) and hath not performed my commandments. And it (1 Sam. 15:35; 16:1) grieved Samuel; and he cried unto the LORD all night.
[It repenteth me] He speaks after the manner of men. It is said that God repents, when He does that which men are wont to do when they repent (Menochius out of Sanchez). Now, men change their plans, or disassemble what they have constructed (Sanchez, Estius). Since God is immutable, most wise, and most blessed, no repentance is properly applicable to Him, as it is said in verse 29; but it repenteth Him, when He recalls and retracts His blessings (Lapide).
It repenteth me: repentance properly notes grief of heart, and change of counsels, and therefore cannot be in God, who is unchangeable, most wise, and most blessed; but it is ascribed to God in such cases, when men give God cause to repent, and when God alters his course and method of dealing, and treats a person as if he did indeed repent of all the kindness he had showed to him.
[Samuel was grieved] Hebrew: it burned, namely, the nose, that is, he was afflicted with grief. It is a καταχρηστικὴ/catachrestic/improper Synecdoche of species, anger in the place of grief; for some anger is grief (Piscator).
[He cried to the Lord] More specifically, so that he might appease Him (Vatablus). Samuel is not ἐπικαιρέκακος, that he would rejoice over another’s misfortunes. Unless he had been a good man, he would have congratulated himself over such a successor. But he prays oppositely, even indeed through the whole night (Martyr).
He cried unto the Lord all night, to implore his pardoning mercy for Saul, and for the people; so far was he from rejoicing in their calamities, as an envious and self-seeking person would have done.
 Hebrew: וַֽיְהִי֙ דְּבַר־יְהוָ֔ה אֶל־שְׁמוּאֵ֖ל לֵאמֹֽר׃  Hebrew: נִחַ֗מְתִּי כִּֽי־הִמְלַ֤כְתִּי אֶת־שָׁאוּל֙ לְמֶ֔לֶךְ כִּֽי־שָׁב֙ מֵאַֽחֲרַ֔י וְאֶת־דְּבָרַ֖י לֹ֣א הֵקִ֑ים וַיִּ֙חַר֙ לִשְׁמוּאֵ֔ל וַיִּזְעַ֥ק אֶל־יְהוָ֖ה כָּל־הַלָּֽיְלָה׃  Hebrew: וַיִּחַר.