Avoid the influence of evildoers and those who ridicule good, and adopt the study and knowledge of Torah as your main goal. Then G-d will reward you with a life of joy good fortune.
The "sinful". A wicked person promotes lawlessness, and disregard for Torah, while the sinful one errs unintentionally. Nevertheless, he too is condemned because his frivolous attitude towards G-d is the cause of his sinfulness.
The Artscroll Tehillim