At first we are not asking «What does it mean to me?»but «What did it mean to the original readers?»; later we can ask, «What does it mean to me?». We have to take into account the historical and cultural background of the author and the recipients.
«3 days & 3 nights»(Mt.12:40) have led some to come up with a "Wednesday crucifixion theory," esp. the cult of Armstrongism. How could Jesus die on Friday afternoon and rise Sunday morning yet "be raised on the third day" (Mt.16:21)? Exact meanings of "three" or "days" won't help explain the apparent contradiction.
We need an historical tidbit: Jews counted any part of a day as a full day, as we would count buckets of water (if there were six and one-half buckets of water, we would say there were 7 buckets of water even if one was only partly full). So to the Jewish mind, any part of a day counted as a full day, and days started at 6 p.m. and ended at 6 p.m. Friday from 3 p.m. to 6 p.m. = day 1. Friday 6 p.m. to Saturday 6 p.m. = day 2. Saturday 6 p.m. to Sunday 5 or so a.m. = day 3. Interpreting within the cultural context keeps us out of trouble.
Gen.15:7-21. The historical context is that cutting animals in two and then walking between the pieces was the normal way of entering a contract in Abraham's day. Both parties walked between, taking the pledge that dismemberment would happen to them if they didn't live up to their part of the contract. But in this case only God goes thru, making it a unilateral covenant.