Since Peter is describing those who are not saved, being "bought" by the Master cannot be referring to what happened at Calvary. Peter was writing to the Jews, most of whom considered themselves as children of God. However, we know from scripture that many who believed they were among the righteous, like the Pharisees, were not.
Look at it this way: If Christ purchased salvation for all, then why would anyone go to hell? Is it because Christ's blood covers all sin except the sin of rejecting the gospel? If that is so, then obviously his sacrifice was insufficient.
God is nothing if not just, and if Jesus did indeed pay for the sins of all, then it would be unjust for God to impose a second punishment on those whose sins were covered the first time. Either Christ's sacrifice is sufficient or it isn't. Calvinism holds that his punishment in our place meets God's requirement of a blood sacrifice for the sins of the elect.
Amen.
"Jesus said unto him, If thou canst believe, all things are possible to him that believeth." -- Mark 9:23
And if we can believe, it is only through the gift of God's grace upon the fallen sinner.
First grace; then belief. Otherwise it's a work of man's ability to believe; something none of us has unless and until He turns us from darkness towards the light.
Salvation is all of God, and none of us; or else it isn't mercy, it's payment due for service (belief) rendered.
Faith is the evidence of our salvation; not a requirement for it.