The expression “poured out” is used often in the Bible. It is used in references to God’s presence being transferred from one place to another. It is God’s desire to transfer His character and attributes to us here on the earth.
In Genesis 28:18 Jacob used a stone as a pillow and had a dream and a message from God. The pouring of the oil on the rock was Jacob saying the presence of God is here.
In Leviticus 28:7 it says that the drink offering is poured unto the Lord.
During the Temple sacrifices blood was poured out on different things as part of the ceremony.
When a man was anointed to a spiritual position, oil was poured on him as a sign that the spirit of God is now on him and he had the ability to operate in this position. Also it was a sign that God was with him.
When it was time for the Holy Spirit to come and dwell on the earth, God used the words “poured out”.