Gumb,
You are correct that Jesus did say that the Greatest Commandment is that The Lord is One, and we must love Him with everything we have:
Mark 12:29-30 (ESV): Jesus answered, "The most important is, 'Hear, O Israel: The Lord our God, the Lord is one. And you shall love the Lord your God with all your heart and with all your soul and with all your mind and with all your strength.'
But, Jesus also declared the following statement:
John 10:30 (ESV): "I and the Father are one."
It is the very same Greek word for "ONE" that is used in both Mark 12:29 and in John 10:30.
Jesus also used the very same word for "ONE" in these verses:
Matthew 23:8-10 (ESV): But you are not to be called rabbi, for you have one teacher, and you are all brothers. And call no man your father on earth, for you have one Father, who is in heaven. Neither be called instructors, for you have one instructor, the Christ.
So, since Matthew 23:8-10 says that Christians have only ONE Teacher and ONE Instructor, the Christ, does that exclude The Father? Does that mean God The Father cannot be our Teacher and Instructor? In the same way, when it says that we have only ONE Father, God in Heaven, does that mean that Jesus cannot be our Eternal Father? (Isaiah 9:6) Or, rather, does it show that when Jesus says something about One of the Persons of the Godhead, it is also true of the other Persons?
Also, in Mark 12:29, Jesus said that The Lord is One. Yet, the New Testament teaches that Jesus is the ONLY Lord and the ONE Lord for Christians:
1 Corinthians 8:6 (ESV): yet for us there is ... one Lord, Jesus Christ, through whom are all things and through whom we exist.
Jude 1:4 (ESV): ... our only Master and Lord, Jesus Christ.
Romans 10:9-13 (ESV): because, if you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For with the heart one believes and is justified, and with the mouth one confesses and is saved. For the Scripture says, "Everyone who believes in him will not be put to shame." For there is no distinction between Jew and Greek; for the same Lord is Lord of all, bestowing his riches on all who call on him. For "everyone who calls on the name of the Lord will be saved."
1 Timothy 6:14-15 (ESV): ... the appearing of our Lord Jesus Christ, which he will display at the proper time--he who is the blessed and only Sovereign, the King of kings and Lord of lords,
Who, then, is our One Lord -- is it the Father (Mark 12:29), or is it Jesus? Or, is it rather BOTH The Father and Jesus? (John 10:30) Or, are Christians polytheists who serve and follow TWO Lords? (Matthew 6:24)
Also, the Scripture that Jesus was quoting in Mark 12:29 was Deuteronomy 6:4, which says:
Deuteronomy 6:4 (ESV): "Hear, O Israel: The LORD our God, the LORD is one.
However, it is very important to realize that the very same Hebrew word for "ONE" used in Deuteronomy 6:4, was also used in the following verse:
Genesis 2:24 (ESV): Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.
Are a man and a wife ONE PERSON, or are they UNITED as ONE?
Jesus also said that everyone must worship only The Lord God:
Matthew 4:10 (ESV): Then Jesus said to him, "Be gone, Satan! For it is written, "'You shall worship the Lord your God and him only shall you serve.'"
Later, however, He said that all must honor The Son to the same degree that they honor The Father:
John 5:23 (ESV): that all may honor the Son, just as they honor the Father. Whoever does not honor the Son does not honor the Father who sent him.
Jesus told people to pray to The Father:
Matthew 6:6 (ESV): But when you pray, go into your room and shut the door and pray to your Father who is in secret. And your Father who sees in secret will reward you.
He later told them to pray to The Son as well:
John 14:14 (ESV): If you ask me anything in my name, I will do it.
Jehovah (Yahweh) proclaimed that He would never share His own glory with another god:
Isaiah 42:8 (ESV): I am the LORD; that is my name; my glory I give to no other, nor my praise to carved idols.
Jesus proclaimed that He has always shared His Father's own glory:
John 17:5 (ESV): And now, Father, glorify me in your own presence with the glory that I had with you before the world existed.
Jesus proclaimed His equality with The Father:
John 16:15 (ESV): All that the Father has is mine ...
John 17:10 (ESV): All mine are yours, and yours are mine, and I am glorified in them.
Jehovah said that He created all things ALONE, BY HIMSELF, and that NO ONE WAS WITH HIM:
Isaiah 44:24 (ESV): Thus says the LORD, your Redeemer, who formed you from the womb: "I am the LORD, who made all things, who alone stretched out the heavens, who spread out the earth by myself,
The New Testament teaches that ALL things were created by means of Jesus and FOR Jesus:
Hebrews 1:10 (ESV): And, "You, Lord, laid the foundation of the earth in the beginning, and the heavens are the work of your hands;
John 1:3 (ESV): All things were made through him, and without him was not any thing made that was made.
Colossians 1:16-17 (ESV): For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities--all things were created through him and for him. And he is before all things, and in him all things hold together.
Who, then, is the Creator? The Father or The Son? Did The Father create all things ALONE, BY HIMSELF? Or did He create all things THROUGH His Son, Jesus? Is it possible that the Yahweh (Jehovah) speaking in Isaiah 44:24 was actually The Holy Trinity?
Why did Jehovah take ALL of the credit for creation in Isaiah 44:24, but God The Father gave ALL of the credit for creation to His Son in Hebrews 1:10?