Getting off subject? I said commerce is what we do. The government is in place to protect our ability to engage in commerce. The Consitution, the BOR, the DOI, all are designed to protect us from a tyrannical government that would deny us our free pursuits - 90% of which involves commerce.
If you'll read the DOI I believe the subject is mostly commerce.
The government must also enforce legal contracts that we enter into with each other and provide for defense.
It is the protection of our freedoms that gives us the opportunity to engage in commerce. Without those freedoms we would have no commerce. Take the extreme example of slavery. Slaves do not have any freedom and therefore can not partake in commerce because all of their possessions are owned by the master. Therefore government' primary objective (which the constitution codifies) is to safeguard our freedoms.