There is in fact one Spirit (Ephesians 4:4); the Father (John 4:23-24), the Son (Ephesians 3:17, Colossians 1:27, 1 John 5:12), and the Holy Ghost (John 7:39, 2 Timothy 1:14).
There is one Lord (Ephesians 4:5); the Father (Matthew 11:25, Luke 10:21), the Son (1 Corinthians 8:6, 1 Corinthians 12:3) and the Holy Ghost (2 Corinthians 3:17).
There is one God (Ephesians 4:6); the Father (1 Corinthians 8:6, Romans 15:6, James 3:9 (kjv)), the Son (Hebrews 1:8-9; John 8:58 w/ Exodus 3:14), and the Holy Ghost (Acts of the Apostles 5:3-4, Romans 8:26-27).
These are the same Spirit, the same Lord, and the same God (1 Corinthians 12:4-6).
Now, read the following in light of these factors.
Eph 4:4, There is one body, and one Spirit, even as ye are called in one hope of your calling;
Eph 4:5, One Lord, one faith, one baptism,
Eph 4:6, One God and Father of all, who is above all, and through all, and in you all.
This is not saying that there is one Spirit, the Holy Ghost, one Lord, Jesus Christ, and one God, the Father.
It is saying that the three are one.
One Spirit (Father, Son, and Holy Ghost).
One Lord (Father, Son, and Holy Ghost).
One God (Father, Son, and Holy Ghost).
The reality is that there is one Lord (Ephesians 4:5) and we know Him to be the Father of our Lord Jesus Christ (Matthew 11:25, Luke 10:21).
However, no one can say that Jesus is the Lord except by the Spirit of truth (1 Corinthians 12:3 (kjv)).
And Jesus is the Lord (1 Corinthians 8:6).
How then is there one Lord if Jesus is not the Father?