John Wesley on 1 Samuel 17:29

A cause - Of my thus speaking? Is this giant invincible? Is our God unable to oppose him, and subdue him? However David is not deterred from his undertaking, by the hard words of Eliab. They that undertake public services must not think it strange, if they be opposed by those from whom they had reason to expect assistance, but must humbly go on with their work, in the face, not only of their enemies threats, but of their friends slights, suspicions, and censures.