Git commit why build container everytime


I want do the continuous integration with jenkins git and docker.

I want that when I commit the code in GIT repository it should copy into the container.

but most of the example shows that when commit the code the rebuild the container everytime I dont want to rebuild the container everytime.

Instead when code commit it directly copy to conatainer which have apache is running so I can get the new code in container.

How I can achieve this ??

I can use the COPY command but its run during when I build the image but what happened when anyboy commit the code in git ?? how this new code copy into container wihtout rebuild the container ??