A field of his possession, i.e. which is his by inheritance, because particular direction is given about purchased lands, Leviticus 27:22. And he saith part of it, because it was unlawful to vow away all his possessions, because thereby he had disenabled himself from the performance of divers duties by way of sacrifice, almsgiving, &c., and made himself burdensome to his brethren. According to the seed thereof, i.e. according to the quantity and quality of the land, which is known by the quantity of seed which it can receive and return. Fifty shekels of silver, not to be paid yearly, till the year of jubilee, as some would have it, but once for all, as is most probable,
1. Because here is no mention of any yearly payment, but only of one payment, and we must not add to the text.
2. Because it is most probable that lands and all things were favourably and moderately valued, so that men might be rather encouraged to make such vows upon just occasions, than to be deterred from them by excessive impositions. But if this were yearly rent, it was an excessive rate, and much more than the land ordinarily yielded. For an omer is but the tenth part of an ephah, Exodus 16:36, and therefore not above a pottle of our measure, which quantity of seed would not extend very far, and in some lands would yield but an inconsiderable crop, especially in barley, which was cheaper than wheat, and which for that reason, among others, may seem to be here mentioned rather than wheat.