The number "two" has two different meanings in the Bible. In most cases "two" indicates a joining together or unification. This is easy to see if we consider the conflicts we tend to have between our "hearts" and our "heads" -- between what we want and what we know. Our "hearts" tell us that we want pie with ice cream for dinner; our "heads" tell us we should have grilled chicken and salad. If we can bring those two together and actually want what's good for us, we'll be pretty happy. We're built that way -- with our emotions balanced against our intellect -- because the Lord is built that way. His essence is love itself, or Divine Love, the source of all caring, emotion and energy. It is expressed as Divine Wisdom, which gives form to that love and puts it to work, and is the source of all knowledge and reasoning. In His case the two aspects are always in conjunction, always in harmony. It's easy also to see how that duality is reflected throughout creation: plants and animals, food and drink, silver and gold. Most importantly, it's reflected in the two genders, with women representing love and men representing wisdom. That's the underlying reason why conjunction in marriage is such a holy thing. So when "two" is used in the Bible to indicate some sort of pairing or unity, it means a joining together. In rare cases, however, "two" is used more purely as a number. In these cases it stands for a profane or unholy state that comes before a holy one. This is because "three" represents a state of holiness and completion (Jesus, for instance, rose from the tomb on the third day), and "two" represents the state just before it.

720. 'Pairs of each' means that in relation to goods they are unholy. This becomes clear from the meaning of that number. A pair or two means not only a marriage (and when the heavenly marriage is meant it is a holy number); it also has the same meaning as six. That is to say, two relates to three in the same way that the six days of labour do to the seventh or holy day of rest. This is why in the Word 'the third day' takes on the same meaning as 'the seventh', and embodies almost the same, the reason being that the Lord's resurrection took place on the third day. This also is why the Lord's Coming into the world and into glory, and also every coming of the Lord, is described by the third day, as well as by the seventh day. The two days which go before therefore are not holy, but in relation to the third are unholy, as in Hosea,

Come and we will return to Jehovah, for He has wounded and will heal us; He has stricken and will bind us up; He will revive us after two days, on the third day He will raise us up, and we shall live before Him. Hosea 6:1-2.

And in Zechariah,

It will be in all the land, said Jehovah, that two parts in it will be cut off and breathe their last, and a third will be left in it. And I will lead the third part through the fire, and I will refine them as one refines silver. Zechariah 13:8-9.

And Psalms 12:6 speaks of silver being purest when it has been purified seven times. These quotations show that just as 'sevens of each' did not mean sevens of each but things that are holy, so 'pairs of each' does not mean two of each but those which in relation to the holy are unholy. Accordingly the meaning is not at all that unclean beasts, or man's evil affections, in relation to clean beasts, or goods, were fewer by a ratio of two to seven; for with man evils far outnumber goods.