Eternal Security 23 - Psalm 139:7-12

Psalms 139:7-12 KJV  Whither shall I go from thy spirit? or whither shall I flee from thy presence? 8  If I ascend up into heaven, thou art there: if I make my bed in hell, behold, thou art there. 9  If I take the wings of the morning, and dwell in the uttermost parts of the sea; 10  Even there shall thy hand lead me, and thy right hand shall hold me. 11  If I say, Surely the darkness shall cover me; even the night shall be light about me. 12  Yea, the darkness hideth not from thee; but the night shineth as the day: the darkness and the light are both alike to thee.

Even in the Old Testament God teaches Eternal Security. Why should it be less certain for us??