Is it not true that "Whosoever calls upon the name of the Lord shall be saved"? In other words, "If" you call upon the name of the Lord you shall be saved.

When Jesus was crying out about Jerusalem "...how I would have...but you wouldn't" was He not stating the truth?

Regarding Piper saying "Christ died for all sinners, so that IF you will repent and believe in Christ, then the death of Jesus will become effective in your case and will take away your sins." All sinners are to be freely offered salvation. Only the elect (unconditionally elected) will have the faith (the condition of salvation) to believe.

Just to have the word "if" in this quote does not make it a false statement. It is true that IF you repent and believe on Jesus that you will be saved. Salvation IS conditional on faith. For those who do not have faith are not saved.

Be careful to not take these quotes out of the context of the entire book (just as arminians do with Scripture) and call the whole book heretical.