Hundred
It's a landmark for a young child to count to 100; it sort of covers all the "ordinary" numbers. One hundred is obviously significant for other groupings: 100 cents is a dollar; 100 yards is a touchdown; 100 years is a century, and the landmark for a very long life. It makes sense, then, that in the Bible, 100 represents fullness or a state of completion, or in some instances simply "much." For instance, people marvel that Abraham had Isaac when he was 100 years old; the number represents the point at which the Lord, when growing up as Jesus, united the human elements of himself with the divine elements and in a sense became "complete.
Genesis 17:1-5
1
When Abram was ninety-nine years old, Yahweh appeared to Abram, and said to him, "I am God Almighty. Walk before me, and be blameless.
2
I will make my covenant between me and you, and will multiply you exceedingly."
3
Abram fell on his face. God talked with him, saying,
4
"As for me, behold, my covenant is with you. You will be the father of a multitude of nations.
5
Neither will your name any more be called Abram, but your name will be Abraham; for I have made you the father of a multitude of nations.
