RESURRECTED WITH / IN HIM.
This is the glorious triumph of the new creation. We were not only crucified and buried with Christ; the Bible says that we were also resurrected with him.
When we are dipped into the water completely, we testify that we died and were buried with Christ Jesus, but when we emerge from the water, we show that Jesus is no longer in the grave, nor are we. We are alive with a brand new kind of life. Paul said;
And hath raised us together, and made us sit together in heavenly places in Christ Jesus.
Ephesians 2:6
That like as Christ was raised from the dead by the glory of the Father, even so we also should walk in the newness of life.
Romans 6:4b
We can walk in the newness of life because we were raised with him in that kind of life.
In summary, the significance of water baptism is to testify before the whole world of our union with Christ in his death and life. We died IN HIM to sin and are now ALIVE IN HIM to God.