in his heart = to himself.
I shall now perish . This lack of faith acted with disastrous results to David. It put him in a false position; shook the People's confidence in him; delayed his own election; and led to divisions in the kingdom.
coast = border.

men . Hebrew. 'enosh. App-14 .

man . Hebrew. 'ish. App-14 .
Nabal's wife. See note on 1 Samuel 30:5

Ziklag . An outpost which protected Gath.

country. Hebrew "field". Put by Figure of speech Synecdoche (of Part) for country. App-6 .

And. Note the Figure of speech Polysyndeton ( App-6 ) in 1 Samuel 27:9 .

Whither . Some codices, with Septuagint and Vulgate, read "against whom".
road = raid.
south. Hebrew the Negeb or hill country south of Judah.

People Israel = Israel's People.