mitsvah (mits-vaw'); from OT:6680; a command, whether human or divine (collectively, the Law):
5 Because that Abraham obeyed my voice, and kept my charge, my commandments, my statutes, and my laws. KJV The verse above took place long before Exodus 20:1, the first of the 10 commandments.
11 And thus shall ye eat it; with your loins girded, your shoes on your feet, and your staff in your hand; and ye shall eat it in haste: it is the LORD's Passover. KJV
14 And this day shall be unto you for a memorial; and ye shall keep it a feast to the LORD throughout your generations; ye shall keep it a feast by an ordinance for ever. KJV
49 One law shall be to him that is homeborn, and unto the stranger that sojourneth among you.
50 Thus did all the children of Israel; as the LORD commanded Moses and Aaron, so did they. KJV
These verses also took place before the 10 commandments were given to Moses.
21 He that hath my commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him. KJV
The first of the 10 commandments is the greatest of all commandments but not the first.