John Gill Commentary 1 Samuel 22:1

"David therefore departed thence, and escaped to the cave of Adullam: and when his brethren and all his father`s house heard it, they went down thither to him." — 1 Samuel 22:1 (ASV)

David therefore departed from thence
From Gath, being driven by Achish from his court, and let go by his servants, and glad he was of the deliverance:

and escaped to the cave Adullam ;
which was no doubt near to a city of the same name in the tribe of Judah, of which (See Gill on Joshua 15:35); this being a strong place, and in his own tribe, he might hope to be in greater safety; here he penned his hundred forty second psalm, see (Psalms 142:1–7) :

and when his brethren and all his father's house heard [it] ;
that he was come thither:

they went down thither to him ;
to visit and comfort him, counsel and assist him all they could; and chiefly to secure themselves from the rage and malice of Saul, who they might fear would fall upon them, and avenge himself on them for David's sake.