"Ki mei Noach zos li...For [like] the waters of Noach shall this be to me" (Isaiah 54:9).
The verse in Yeshaya refers to the Deluge as "mei Noach" (the waters of Noach). In light of the fact that the deluge erased all of mankind save Noach and his family, this is hardly a complimentary association. In fact, according to the Zohar Hakadosh, this verse issues a stunning indictment of Noach. When Hakadosh Baruch Hu informed Noach of the impending destruction of the world, Noach should have prayed. The verse in Yeshaya indicts Noach for his inaction and apathy by referring to the Deluge as mei Noach.
Concern for one's fellow man is a universal obligation. Noach, after all, was a ben Noach (Noachite).
The obligation for concern runs even deeper for Jews vis-a-vis each other. The Torah mandates mutual responsibility and interdependence amongst Jews - kol Yisroel areivim ze bozeh; Jews exist symbiotically. We are not merely responsible for each other (arev in the sense of guarantor); we are "mixed up with each other", symbiotically intertwined (arev in the sense of mixture).
This obligation clearly extends beyond prayer. It entails teaching, reaching out, philanthropy, acts of kindness, etc. - anything which helps to foster Torah observance for every Jew.
We, as Jews, have always desperately needed each other. This existential truth is more relevant than ever today when we are ravaged by assimilation. The rate of intermarriage, rachmana litzlan, is, at least, fifty percent. An all-too small minority of Jewish children receive a Torah education. Even in Torah observant circles the need is great. "Inreach" ought to be a priority. Sadly, amidst unprecedented affluence, poverty - even dire poverty - persists. The list goes on and on.
There is no question that there are virtually countless causes which need our involvement and/or financial support. There is no question that there are virtually countless avenues (outreach, "inreach", education, strengthening our shuls, chessed, philanthropy...) for fulfilling the mandate of kol Yisroel areivim. The question is if every one of us, in accordance with his/her individual talents and resources, is fulfilling that mandate. To do less rachmana litzlan would invite the indictment of mei Noach.