I like these verses because they have a nice answer to the question “Why do we do these commandments?” Actually, there are several answers, only implied and three stated.
20 And when thy son asketh thee in time to come, saying, What mean the testimonies, and the statutes, and the judgments, which the Lord our God hath commanded you?
21 Then thou shalt say unto thy son, We were Pharaoh’s bondmen in Egypt; and the Lord brought us out of Egypt with a mighty hand:
22 And the Lord shewed signs and wonders, great and sore, upon Egypt, upon Pharaoh, and upon all his household, before our eyes:
23 And he brought us out from thence, that he might bring us in, to give us the land which he sware unto our fathers.
24 And the Lord commanded us to do all these statutes, to fear the Lord our God, for our good always, that he might preserve us alive, as it is at this day.
25 And it shall be our righteousness, if we observe to do all these commandments before the Lord our God, as he hath commanded us. (Deut. 6:20-25)
The first one is implied. Because the Lord brought us out of Egypt miraculously and to a promised land [we owe Him allegiance and fealty.]
The next are stated.
2) “for our good always” – The commandments are for our good.
3) “that he might preserve us alive” – The commandments continue the Lord’s work of salvation in our lives, both temporally and spiritually. They restrict us from harmful acts and require us to do things that help us grow.
4) “it shall be our righteousness, if we observe to do all these commandments” – Obedience leads to a change for the better when coupled with faith in Christ’s atonement.
It is always interesting to see how different people explain the necessity of keeping the commandments of God. There are so many ways the commandments bless us that keeping them always seems like an adventure. It's a cheerful thing to live obediently in hope of seeing how the Lord will bless us even if we’re not sure how.