I'm sorry, but you are wrong on just about every aspect of your thread.
First off, I said nothing about sins being dead or alive. I have no idea why you made that comment. I DID say we need to repent of dead works. This was the primary stumbling block for the Jew, and what Jesus was talking about.
Hebrews 6:1 New King James Version (NKJV)
The Peril of Not Progressing
6 Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation of repentance from dead works and of faith toward God,
Secondly, if we are talking about the first words Jesus spoke, what you posted are at least the 3rd recorded words.
This one when He was 12:
Luke 2:49 New King James Version (NKJV)
49 And He said to them, “Why did you seek Me? Did you not know that I must be about My Father’s business?”
This, when He was an adult:
Matthew 3:15 New King James Version (NKJV)
15 But Jesus answered and said to him, “Permit it to be so now, for thus it is fitting for us to fulfill all righteousness.” Then he allowed Him.
Lastly, EVEN the verse you quoted doesn't fit the narrative that we have to follow any Law, or that Jesus' Sacrifice ALONE isn't sufficient for Salvation. Mark expounds upon the verse:
Mark 1:15 New King James Version (NKJV)
15 and saying, “The time is fulfilled, and the kingdom of God is at hand. Repent, and BELIEVE IN THE GOSPEL.”