Complex sentence: The function of the Court is "to ensure the observance of the engagement undertaken" by the contracting states in relation to the Convention and its protocols, and therefore to ensure the implementation of the Convention by these states.
Split into simpler sentences: The function of the Court is "to ensure the observance of the engagement undertaken" by the contracting states in relation to the Convention and its protocols. This means that the Court has to ensure the implementation of the Convention by these states.