The resolutions are typically adopted upon a finding by the Council of threats to international peace and security, such as from various forms of terrorism. See The Role of Security Council. Council on Foreign Relations, https://www.cfr.org/backgrounder/un-security-council (August 12, 2021); see also https://www.un.org/en/our-work/maintain-international-peace-and-security#:~:text=Under%20Chapter%20VII%20of%20the,Operations%20and%20Special%20Political%20Missions (discussing the role of the Security Council in maintaining international peace and security). The treaties are negotiated and ratified by Members States under the UN umbrella in response to a need for cross-border action to tackle problems like terrorism and corruption, which by their nature do not respect national boundaries. Knowledge of and adherence to the international instruments and standards, as a practical matter, will often make your job easier. For example, if your national jurisdiction ratifies an international instrument, as a prosecutor you will receive assistance pursuant to that treaty from all other States which have ratified it, enhancing your ability to receive international assistance and facilitating the prosecution of your cases. See International Law Aspects of Countering Terrorism, https://www.unodc.org/documents/terrorism/Publications/FAQ/English.pdf
In addition, knowledge of and adherence to Security Council resolutions and the work of the Council regarding, for example, terrorism and the threat posed by specific groups such as ISIL or Al-Qaeda, will inform you as to the threat posed by these groups in your region and national jurisdiction, which can be useful in the investigation and prosecution of cases. Further, adherence to the resolutions by Member States can help to lessen the threat these groups pose to international peace and security, thereby benefitting the global community.