It is important that we understand that there is only one being speaking the Word Of The Lord.   That being is our Lord, Jesus Christ.   He is the Incarnate Word of God.   He eternally preexisted with the Father (Holy Spirit) before His taking on human flesh.   

The Father (Holy Spirit) is the unction for the Word Of The Lord but the Son (Christ Jesus) is the one who speaks it.   

Because there were different people involved in different dispensations, different terms have been used to reference the Lord.   We see this in the different names that were used to reference our Creator in the pentateuch.   

The Hebrews knew the Lord as YHVH (anglicised as Jehovah), the breath of life.   They respectfully disdained to call Him YHVH and so used the term, Lord, instead.   

Since the Hebrews rejected Jesus as Messiah a rift came between the Old Testament and the New Testament in the minds of Bible readers.   We all know that the Hebrews believe in YHVH, but since they rejected Jesus (Jeshua) as Messiah, who is Lord of Lords and King of Kings, Christians could not help but think of there being two distinct Gods - Jehovah and Jesus (different persons if you like).   

With the Baptism of the Holy Spirit being poured our on the day of Pentecost, there was yet another manifestation of God to contend with - at least in the minds of people who could not grasp the omnipresence or ubiquitousness of the Lord who is first and foremost Spirit.   

The Holy Spirit is the Spirit Of God.   Since Jesus is God, then the Holy Spirit is the Spirit Of Christ.   

So the Word Of The Lord is conceived by the Holy Spirit of Christ Jesus and spoken by Christ Jesus, the physical presence of the Holy Spirit.   The fact that Jesus was not known by that name in the Old Testament should not confuse us.