The Bible gives us examples of different Christians and shows us that God’s Grace is sufficient for us all.
The old time Christian
In one sense we have those that had accepted Christ from the very beginning (essentially). They may have been born into a Christian family, grown up knowing Christ, but they still have troubles, still might stumble (e.g. Peter ) but remain under Grace and are forgiven. Peter denied Jesus not once, not two but three times! Peter was one of the most dedicate disciples and was adamant he wouldn’t do such a thing. But he did. Nevertheless, Peter was used greatly in the foundation of the Church.
The new Christian
We have those who may have been unconcerned with Christianity, lacking knowledge of Jesus, or against Christianity. They may have done everything under the sun but they are still worthy of God’s Grace because it is sufficient (e.g. Paul). Paul persecuted Christians before he accepted Christ but this didn’t make him any less worthy when he did.
It doesn’t matter when you accepted Christ or what you did before then. We are transformed when we come to Christ and the old passes away (2 Corinthians 5:17).
It does matter what we do after but that’s not to say we will never slip up again (and also not to say we should sin on purpose just because God doesn’t expect us to be perfect). We are imperfect made perfect by God. That’s why we need His Grace.