1)
Why should you through tie them on your heart constantly?
1.
Malbim: Even though Mitzvos are far from the heart's nature, tie them with ropes, so they will be tied constantly. Tilt your heart, the power that rules over the body, to guard them.
2)
What is "Andem [Al Gargerosecha]"?
1.
Rashi: It is an expression of tying, like "E'endenu Ataros Li" (Iyov 31:36).
2.
Malbim: Speak in Mitzvos constantly. Via repetition, they will be guarded for you also in the heart.
