Albert Barnes on John 10:12

A hireling. A man employed to take care of the sheep, to whom wages is paid. As he does not own the sheep, and guards them merely for pay, rather than risk his life he would leave the flock to the ravages of wild beasts. The word translated hireling is often employed in a good sense; but here it denotes one who is unfaithful to his trust; and especially those ministers who preach only for support, and who are unwilling to encounter any danger or to practise any self-denial for the welfare of the church of God. They are those who have no boldness in the cause of their Master, but who, rather than lose their reputation or place, would see the church corrupted and wasted by its spiritual foes.

Whose own the sheep are not. Who does not own the sheep.

(k) "leaveth the sheep" Eze 34:2-6, Zech 11:17