I believe that you are referring to Matthew CH. 9 v 17 "Neither
do men put new wine into old bottles: else the bottles break, and
the wine runneth out, and the bottles perish: but they put new wine
into new bottles, and both are preserved".
What Christ is teaching his disciples here is that you cannot
teach an old dog new tricks. In other words some people are so used
to the teachings of the gospel that they have been taught, that to
give them a new doctrine would be hard for them to accept, and in
doing so may break the spirit which they already have. To teach
them new teachings would cause their minds to become confused.
This is why Christ said that the new wine ( His New Gospel) must
be put into new bottles (Minds that would not become confused).