Two approaches to Olam Haba

סנהדרין דף קיא ע"א

"לכן הרחיבה שאול נפשה ופערה פיה לבלי חוק"
אמר ר"ל- למי שמשייר אפי' חוק אחד
אמר לו יוחנן- לא ניחא למרייהו דאמרת להו הכי אלא לא למד אפילו חוק אחד

  

Sanhedrin 111a 

"Hell shall widen its mouth and swallow those without Law" (Yeshayahu 5:14)
Rish Lakish said: Hell swallows those who neglected even a single Law.
Ribbi Yochanan told him: God doesn't appreciate that you judge His people so harshly. Rather, the pasuk means as follows- Hell swallows up only those who wouldn't even observe a single Law.

A"A says that we see here two distinct approaches to olam haba. In Rish Lakish's paradigm, Hell has an all-or-nothing nature. If you screw up once, you're out of the race. Ribbi Yochanan flips it. Observing even one mitzvah is enough to keep you out of Hell.
As we have discussed previously, the Rambam's approach (as presented in Perush Hamishna Makot 3:17) is consistent with Ribbi Yochanan.

(It is worth noting that all this is only relevant when discussing God's account of our observance. Between man and his fellow, those who outright reject even a single mitzvah of the Torah are given the halachic status of "meshumadim" (Rambam Hil' Teshuva 3:9).)