Why were the baptisms required for Israel?
Exodus 19:5 Now, therefore, if you will obey my voice indeed and keep my Covenant, then you shall be a peculiar treasure unto me above all the people, for all the Earth is mine. And you shall be unto me a kingdom of priests and a holy nation. These are the words which thou shalt speak unto the children of Israel.
Exodus 19 is when Moses begins to give the Old Testament law to Israel, and he tells them right up front, God's intention with Israel is to make them a kingdom of priests.
Lev 21:16-21 And the LORD spake unto Moses, saying, (17) Speak unto Aaron, saying, Whosoever he be of thy seed in their generations that hath any blemish, let him not approach to offer the bread of his God. (18) For whatsoever man he be that hath a blemish, he shall not approach: a blind man, or a lame, or he that hath a flat nose, or any thing superfluous, (19) Or a man that is brokenfooted, or brokenhanded, (20) Or crookbackt, or a dwarf, or that hath a blemish in his eye, or be scurvy, or scabbed, or hath his stones broken; (21) No man that hath a blemish of the seed of Aaron the priest shall come nigh to offer the offerings of the LORD made by fire: he hath a blemish; he shall not come nigh to offer the bread of his God.
According to Leviticus 21, there were some obvious requirements placed upon the priests who were to approach to offer the offerings of the Lord. They had to be a perfect physical specimen.
