All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Among the meanings of the word “Fundamental” are the principle, the basis, the foundation of something, but this does not necessarily mean that this thing is a Waajib (an obligation). So, there is nothing wrong if ‘fundamental’ is used for something that is recommended or desirable.
Indeed, helping people is one of the important matters of religion and one of the greatest acts of worship by which one gets closer to Allaah. Ibn 'Umar narrated that a man came to the Prophet and said: "O Messenger of Allaah, which people are most beloved to Allaah? And which actions are most beloved to Allaah?" The Prophet said: "The most beloved people to Allaah are those who are most beneficial to the people, and the most beloved acts of worship to Allaah is a happiness which you bring to a Muslim, or that you take him out of a difficulty, or pay off his debt, or feed him when he is hungry, and it is more beloved to me that I walk with a Muslim brother to achieve his need than I perform I'tikaaf (seclusion) in this mosque (Masjid An-Nabawi in Al-Madeenah) for a whole month…”[At-Tabaraani]
However, helping people is in principle something recommended or desirable, but it can be an obligation in some cases as stated by the scholars. Al-Jassaas from the Hanafi School of jurisprudence, said: “Every person is obliged to save others if he fears their death, like if he sees a man who is targeted by others to kill him, or fears that he would drown while he can save him.” Moreover, Al-Mardaawi from the Hanbali School of jurisprudence, said in Tas-heeh Al-Furoo’: “He is obliged to save him if he is able to do so.”
Perhaps it is appropriate here to clarify the difference between the Rukn (pillar) and the Waajib (obligation): they are the same in the sense that both of them are obligatory, but the difference between them is that the pillar is part of the entity of something which cannot exist without it, contrary to the Waajib, without which something can exist while the person becomes sinful for not doing it.
Allaah Knows best.