Mind and heart. That is, a person enjoys and delights in the fact that the Creator has given him a place for faith. Also, he is happy that the Creator has given him a place of work in the heart.
“When a man regrets, what does the Shechina [Divinity] say? ‘It is lighter than my head and than my arm.’” This means that a person regrets the fact that the Creator wants people to serve Him in a manner of faith and would be happy if we could work in the manner of knowing. Also, a person is sorry that we were forbidden to use the will to receive.
The answer to this is “It is lighter than my head,” meaning that the work I gave you in the mind, I could certainly give you work in a manner of knowing but I chose the path of faith, for by this they will be able to achieve the goal, which is to do good to His creations.
It is likewise with work in the heart that a person is commanded to do, as it is written in placing the head-Tefillin next to the brain, and on the arm, the stretched out arm, which is next to the heart. “Lighter than my head” means that they think that the way I gave them is a way of ignominy. However, we must believe that this is the best way that the Creator has given us, and we must be happy about it.