Seven (7) is a "magic" number. In the teaching of the Catholic church, there are seven corporal and spiritual works of mercy:
- To feed the hungry;
- To give drink to the thirsty;
- To clothe the naked;
- To harbour the harbourless;
- To visit the sick;
- To ransom the captive;
- To bury the dead.
The spiritual works of mercy are:
- To instruct the ignorant;
- To counsel the doubtful;
- To admonish sinners;
- To bear wrongs patiently;
- To forgive offences willingly;
- To comfort the afflicted;
- To pray for the living and the dead. http://www.newadvent.org/cathen/10198d.htm
There are also 7 Capital Sins (Anger, envy, lust, pride, gluttony, sloth and covetousness) and 7 Cardinal Virtues and oppose them (Faith, Hope, Charity, Fortitude, Justice, Temperance, Prudence).
While interesting, I don't think this has anything to do with the Commandments in Animal Farm. There may have been 3, 4, 7 , 10 or 12 (other numbers often called magic). Their importance is that they refer to behaviors that at first seem beneficial to the people but which, through the addition or subtraction of a couple words, could be used to support the position of the dictators (pigs).
Orwell shows how uncertain "truth" is, and vigilant we must be to protect our knowledge, and how easy it is for manipulate the past (especially with animals whose life span is much shorter than ours so that very few of the "original" animals were alive at the end to recall what the original commandments were).