Here is the exchange made of the Levites for the first-born. 1. The first-born were numbered from a month old, Num. 3:42 , 43 . Those certainly were not reckoned who, though first-born, had become heads of families themselves, but those only that were under age; and the learned bishop Patrick is decidedly of opinion that none were numbered but those only that were born since their coming out of Eg...