{He began to teach them} ((8872)xato didaskein autous). Mark
is fond of this idiom, but it is not a mere rhetorical device.
 Mt 16:21  expressly says "from that time." They had to be told
soon about the approaching death of Jesus. The confession of
faith in Jesus indicated that it was a good time to begin. Death
at the hands of the Sanhedrin (elders, chief priests, and
scribes) in which Pharisees and Sadducees had about equal
strength. The resurrection on the third day is mentioned, but it
made no impression on their minds. This rainbow on the cloud was
not seen. {After three days} (meta treis h(886d)eras).  Mt 16:21 
has "the third day" (	(8869) trit(8869) h(886d)er(8369)) in the locative case
of point of time (so also  Lu 9:22 ). There are some people who
stickle for a strict interpretation of "after three days" which
would be "on the fourth day," not "on the third day." Evidently
Mark's phrase here has the same sense as that in Matthew and Luke
else they are hopelessly contradictory. In popular language
"after three days" can and often does mean "on the third day,"
but the fourth day is impossible.