31. whatsoever cometh forth of the doors of my house to meet me--This evidently points not to an animal, for that might have been a dog; which, being unclean, was unfit to be offered; but to a person, and it looks extremely as if he, from the first, contemplated a human sacrifice. Bred up as he had been, beyond the Jordan, where the Israelitish tribes, far from the tabernacle, were looser in their religious sentiments, and living latterly on the borders of a heathen country where such sacrifices were common, it is not improbable that he may have been so ignorant as to imagine that a similar immolation would be acceptable to God. His mind, engrossed with the prospect of a contest, on the issue of which the fate of his country depended, might, through the influence of superstition, consider the dedication of the object dearest to him the most likely to ensure success.
      shall surely be the Lord's; and [or] I will offer it up for a burnt offering--The adoption of the latter particle, which many interpreters suggest, introduces the important alternative, that if it were a person, the dedication would be made to the service of the sanctuary; if a proper animal or thing, it would be offered on the altar.

JFB.