John Calvin on Genesis 24:5

5. And the servant said unto him. Since he raises no objection respecting Isaac, we may conjecture that he was so fully persuaded of his integrity as to have no doubt of his acquiescence in his father’s will. We must also admire the religious scrupulosity of the man, seeing he does not rashly take an oath. What pertained to the faithful and diligent discharge of his own duty he might lawfully promise, under the sanction of an oath; but since the completion of the affair depended on the will of others, he properly and wisely adduces this exception, “Peradventure the woman will not be willing to follow me.”