Entered into. In the first line, it is appropriate to state that the agreement is entered into. If you enter into something such as an agreement, discussion or relationship, you become involved in it. An agreement is a psychological meeting of minds resulting from offer and acceptance (i.e. the mental consent required under all European laws to have an agreement) that is eventually reflected (as well as possible) in the wording of a contract.
To make an agreement. In the U.S. common law, an agreement is conceptually considered to reflect a bargain between the parties. This might explain that, since a bargain is ‘made’, drafters use is made as a lead-in. The words is made strongly reflect the objective nature of an agreement: distinct and separate from the minds of the parties. It probably also explains why an entire agreement clause has a relatively strong effect (in view of the legal concept of the parol evidence rule, the explanation of which is outside the scope of this book).
Pragmatically simple. Whatever your preference is, is made and entered into are largely redundant. It is appropriate not to start the contract with an introductory line (which includes the title, a date and the parties’ names and details) but to leave it open and to simply use a heading “THE PARTIES:”