Dhammapada 1:2

Mind is the forerunner of all actions.
All deeds are led by mind, created by mind.
If one speaks or acts with a serene mind,
Happiness follows,
As surely as one's shadow.

Dhammapada 1:2 Twins

I am going to skip the redundancy here of the first statement. I believe it is there to drive home the understanding a bit more.

If one speaks or acts with a serene mind,
happiness follows,
As surely as one's shadow.

If we can calm our mind and help to find serenity then happiness will have no where else to go but to us. Just like our shadow. Unless we are in total darkness then we cannot escape our shadow. It follows us very closely, it does what we do. So can happiness. It will permeate our lives. The key is to guide our minds to a place of serenity. Easier said than done, but it is achievable, as we will see how later.