Basically the first sentence of the first section defines it:
"Das Entsendegesetz verpflichtet ausländische Arbeitgeber zur Einhaltung von minimalen Lohn- und Arbeitsbedingungen gemäss den anwendbaren schweizerischen Vorschriften."
Google translate gives this:
"The Posting Act requires foreign employers to comply with minimum wage and working conditions in accordance with the applicable Swiss regulations."
In reality this law is not needed or applied, if it wouldn't be there, nothing would change. The minimum wage is not enforced but is in place implicitly, at least this is what I observe.