1 Samuel 19:5
For he did put his life in his hand, and slew the Philistine, and the LORD wrought a great salvation for all Israel: thou sawest it, and didst rejoice: wherefore then wilt thou sin against innocent blood, to slay David without a cause? For he did put his life in his hand, and slew the Philistine, and the LORD wrought a great salvation for all Israel: thou sawest it, and didst rejoice: wherefore then wilt thou sin against innocent blood, to slay David without a cause?
The verse belongs to the time after David killed Goliath, when David remained with Saul and Jonathan made a covenant with David and loved him as his own soul. To put life in the hand means to risk life, which David did when he slew the Philistine. Through David the Lord worked a great salvation and deliverance for all Israel, which Saul saw and rejoiced in. Jonathan appeals to that service as the reason Saul must not sin against innocent blood by slaying David without cause. The same risking of life applies to undertaking work in the South, where prejudice and sudden violence could bring destruction of property and loss of life.