What is the ruling on celebrating religious occasions such as the Isra and Mi'raj and the Prophet's birthday by holding seminars and lectures merely to commemorate them, while avoiding bid'ah (innovations) such as mawlids (celebrations involving specific rituals or practices)?

Originally, delivering lectures and seminars to remind people of a certain occasion is permissible. However, repeating this always whenever the occasion comes makes it an Eid (festival), and in Islam, there are only two Eids prescribed by Allah. A Muslim should always remember the major events in the life of the Prophet, peace and blessings be upon him, and emulate him, and not make his religion a religion of occasions. It was not from the practice of the Salaf (early Muslims) to repeatedly celebrate these events.