Musar על קידושין 78:7

Whenever it is spelled as Tov the reference is to the manifest good. When it is spelled Tuv the reference is to the hidden good. [The author discussed this in Parshat Ba'halotecha, in connection with Moses' offer to Yitro to join the Jewish people. Ed.] In connection with Torah we find the word spelled טוב with both the vowels חולם such as in Proverbs 4,2: כי לקח טוב נתתי לכם, as well as in Psalms 119,72: טוב לי תורת פיך. It is also spelled with a שורוק as in Psalms 119,66: טוב טעם ודעת למדני. In connection with ארץ ישראל we find ארץ טובה in Deut. 8,7 spelled with the vowel חולם, whereas in Isaiah 1,19 we are promised by the prophet "טוב הארץ תאכלו," spelled with the vowel שורוק. With respect to עולם הבא, we find in Deut. 5,16: למען ייטב לך, which our sages (Kidushin 39b) explain as a reference to a world which is totally good.