Property law encourages people to maximize the value they derive from their property by preventing involuntary appropriation.
Contract law prevents opportunism in exchanges involving the passage of time.
The early view was that a promise is legally enforceable if it is part of a bargain. Of these three, consideration is the least straightforward. In the context of contracts, consideration consists of something the promisee gives the promisor in exchange for the promise. The presence of consideration was required to make a contract enforceable. The promisor is giving something to the promisee in the future in exchange for something the promisee gives the promisor now.