The greatest gift is that God is prepared to forgive our sins through Jesus not only at the point of salvation but on a daily basis, if we ask him to and confess our failing. We still live with this old nature and we can still sin although not on purpose like the person who doesn’t believe. Sin is corruption and we don’t wont any part of it. The hardest part is forgiving others who sin against us.
What you don’t want as a Christian is a hard heart, you can get this by sinning outside the grace of God (willfully), you don’t give any thought to your conscience and just do what you think is alright. This will lead you further and further away from God and who knows where. An example of this would be just living with your “partner” and not marrying because marriage is just a piece of paper afterall.