Albert Barnes Commentary Jeremiah 38:16

"So Zedekiah the king sware secretly unto Jeremiah, saying, As Jehovah liveth, that made us this soul, I will not put thee to death, neither will I give thee into the hand of these men that seek thy life." — Jeremiah 38:16 (ASV)

That made us this soul - This very unusual addition to the formula of an oath (1 Samuel 20:3) was intended to strengthen it. By acknowledging that his soul was God’s workmanship Zedekiah also implied his belief in God’s power over it.