When you click "Publish" from the Actions menu of the Contract Attributes, a contract will have a status of Pending until the date when the Effective Date of the contract becomes in force. At that time, then, the status changes to Published. So, you can publish a pending contract, but it goes into a different status until the contract is actually effective.
The significance of this is that, in reporting and searching, you can list Pending and Published (Active) contracts separately, as required in certain types of contract audits. Alternatively, you may want or need to search for or report on both contracts that are Published and contracts that are Pending to get a full picture of the company's contractual obligations at a particular point in time - after all, that snow removal is still an active contract, even though it's not snowing yet. So, you can report on the 2 statuses separately or together; you just need to be aware of the difference in status.
Your contract should publish just fine, it'll simply be in Pending status until it reaches the Effective Date.