Three is the number of perfection, or completion. This number is repeated throughout the Bible as a symbol of completeness.
God's attributes are three: omniscience, omnipresence, and omnipotence.
Time is divided in three: past, present and future.
Three is the first of four perfect numbers...
Three denotes divine perfection;
Seven denotes spiritual perfection;
Ten denotes ordinal perfection; and
Twelve denotes governmental perfection.
Abraham offered three measures of meal to his guest(s), showing the perfection of God's divine nature. In Numbers 15:9, the instructions to offer with a burn offering read, "Then shall he bring with the bullock a meal offering of THREE tenth deals of flour.", as were the instructions for the cleansing of a leper in Lev 14:10.
The third book in the Bible, where we learn about true worship, is Leviticus.
During His ministry Jesus raised three persons from the dead.
On the third day, the earth rose from the water, symbolic of resurrection life. He was crucified at the third hour, was on the cross from 3 hours, rose from the grave on the third day.
The inscription above His cross, in three languages, showed the completeness of His rejection by man.
He fulfilled the three offices of Prophet, Priest, and King (Deut 177:15, 18:3-5, and 18:15).
For more on the number three, please reference EW Bullinger's excellent book Number in Scripture.