The mishna quoted above from Chulin 130a states that if an animal was consecrated as holy to God and then it was maimed or otherwise damaged in a way that made it not fit for an offering, still it is holy and must always be treated as such.
From this we can learn that the Jewish people who were first consecrated. Even if they were to now stray from HaShem, they are still eternally Holy.
We might be tempted to think about ourselves that while we might have been pure in our youth we are too far gone now to be redeemed.
This mishna teaches us the opposite. Since each of us bears a holy soul. Holy even from before our birth, none of our acts no matter how awful justify us in accepting our current seemingly contaminated state.
How do we obtain this state of holiness and purity we've lost? The first step is realizing it can't be lost. The second step is treating yourself now as the holy and pure person you are within.