Answer:
That phrase is simply re-itterating that you've signed a binding contract. A (blank) is a (blank) is a (blank) is a phrase that is used when someone wants to re-itterate that fact that the blank is in existence or of relevence, no matter what condition is presented. For intance, "a bird is a bird is a bird" means that no matter what the circumstance, a bird will always be a bird.
This is called an "extended tautology." The statement "a contract is a contract" implies that it cannot be simply abrogated by one party or the other. For example, one party addressing the other party who does not want to be bound by it. The 3-part version is emphasizing this, in some cases pedantically, to stress the point.