Question

why is the birth of Christ significant to count historical timeline

Answer 1

Augustus was the first Roman ruler to be worshiped as a son of a god (divi filius), and the day of his birth was considered the beginning of his glad tidings or "gospel" for the world.

Answer 2

There is an absolute reason behind it please take a note of it actually the moder era or the era after jesus christ is highly dominated by the christians. As you can see that the UNITED KINGDOM annexed many of the country and set up their rule they have huge no. Of colonies this dominance of the world at that time is the reason why we consider it.