The Catechism in Questions & Answers

261. How is blessing attained, and how does it unfold?

God often imparts His blessing through human beings who have been commissioned by Him to this end. No one can bless himself.
Blessing can unfold when it is grasped in faith. Whether it has enduring effects also depends on the attitude and conduct of the person being blessed. Blessing is a gift of God that can always be renewed. Blessing can, however, also extend beyond the person who received it to future generations.