People say God is three in one, but Jesus, the Son, says the new covenant is not his but the Lord's. Aren't they the same thing?
Usually these questions are easier to figure out if you read the actual verse.
Jesus said that his words are no different from the Father's.
- "He who rejects Me, and does not receive My words, has that which judges him--the word that I have spoken will judge him in the last day. For I have not spoken on My own authority; but the Father who sent Me gave Me a command, what I should say and what I should speak. And I know that His command is everlasting life. Therefore, whatever I speak, just as the Father has told Me, so I speak" (John 12:48-50).
- "Jesus answered them and said, "My doctrine is not Mine, but His who sent Me"" (John 7:16).
- "Jesus answered and said to him, "If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our home with him. He who does not love Me does not keep My words; and the word which you hear is not Mine but the Father's who sent Me" (John 14:23-24).
These statements are not saying that Jesus would teach anything different from the Father. He is emphasizing that his teachings and the Father's are the same. But that is because God is one (perfectly united). You would not expect to hear anything different between the Father, the Son, or the Spirit.
Since Christ is given all authority in this age, "And Jesus came and spoke to them, saying, "All authority has been given to Me in heaven and on earth"" (Matthew 28:18), the law or covenant that Jesus' established is known as his. "Bear one another's burdens, and so fulfill the law of Christ" (Galatians 6:2). Also because Jesus holds all authority, the term "the Lord" typically refers to Christ since he is our ruler.