Romans 6:3-5 (KJV)
3 Know ye not, that so many of us as were baptized into Jesus Christ were baptized into his death?

4 Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.

5 For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection:

To be Baptized into Jesus Christ is to be Baptized into his death . That's the significance . But there you have the thief on the cross dying with Jesus because he died believing in Jesus . He's already on the cross paying for his own iniquities and yet , BELIEVED. And would be buried like Jesus BUT IN CHRIST and so demons can't touch him. The wages of sin is death . Jesus died for us , but the thief died for his iniquities BELIEVING. That's why Jesus accepted him in because Jesus was going to the dead to preach SALVATION, to save the souls trapped in death