It is not heresy to say that Christ died 'for all' in the sense of His Words in the holy Gospel of St. John, chapter 3, where Our Lord says,
"For God sent not His Son into the world, to judge the world, but that the world may be saved by Him."[/color]
In other words, in the sense that Christ's death is SUFFICIENT to save every person who ever lived, then it is most fitting to say that He died 'for all'.
In the Words of the Consecration, however, Our Lord specifically said, "For this is my blood of the new testament, which shall be shed for many unto remission of sins.[/color]
In this case, Our Lord intended to express the EFFICACY of His Sacrifice, that is, the merit that would actually be applied to souls. He was stating that there were ALREADY souls in existence for whom His Sacrifice would ACTUALLY be salvific, and not just potentially so.
This issue is actually one of the main conflicts within Protestantism as well; there are those who insist, wrongly, that Christ died for all, so all are saved, no matter what they may or may not do in terms of faith. This, of course, is heresy.
Then there are those who say that Christ died ONLY for His elect, a definite, foreordained number, and that all those (and ONLY those) elect will somehow, eventually, come to public, professed faith in Christ. Those elect will then NEVER be able to fall away from the faith, a notion which Scripture denies clearly. MOST of these, usually called 'Calvinists', confess that Christ's death was SUFFICIENT to save ALL, but EFFICACIOUS ONLY in the salvation of the elect. This is heretical because it is clear from Scripture that many can and do fall away from the faith, and the Calvinistic heresy teaches that there is need to confess and repent of sin, yet there is no way that any of said sin can possibly be symptomatic of one's rejection of the faith. There are those among the Calvinists who even believe that a man, who PUBLICLY REPUDIATES his faith in Christ and lapses into the gravest sins, MAY still be saved because he MAY be one of the 'elect', and that God will certainly still somehow save that man. What nonsense, and all because they have rejected the ONLY avenues through which God restores sanctifying grace to a soul, namely, His Sacraments.
There are also Protestants who believe that it is man's duty to cooperate with God's offer of salvation through Christ's Cross, but that once a person has made a 'profession of faith', usually via a 'sinner's prayer' of some sort, they are irrevocably and eternally saved, even if they fall into pertinacious and grave, scandalous sin. Obviously, this is heresy of the basest sort, not only because it allows for imprudent lifestyles, but because it engenders smug self-satisfaction (I prayed the prayer, so I know I'm saved, even if I go kill ten people right now and then shoot myself). [NOTE: Yes, I have actually heard Prot 'preachers' and congregants say that very thing, or things just like it.]
Finally, there are those among the Protestants who believe that Christ died a death, again, SUFFICIENT for all but EFFICIENT for many who would make a profession of faith. This profession of faith is an effort engendered by and motivated by God alone, yet in no sense violating man's free will. They believe that while a man can be saved through the graces which God gives through His Church, some also believe that men CAN (and often do) fall away from the faith. They believe that confession (after a sort) and penance (in terms of a determination to reform one's life) are necessary to be restored to right relationship with God. These Protestants also believe that it is possible for someone to fall away entirely and die in their sin, thus being sent to Hell.
Oddly, that last group, although their theology most closely mirrors that of Holy Church, is considered the most bizarre and legalistic of the larger Protestant groups. Several major denominations believe what was expressed in the previous paragraph, and yet, those who claim to be the heirs of the 'Reformation' are insistent that the above statements are heretical and most often not even worth of consideration.
Again, it is certainly true that Christ died for all in the sense that all are WELCOME to come to Him, and all MAY be saved by the merits of His Cross and Resurrection, but only those who ACTUALLY DO SO, whose true disposition of faith is known to God alone, will actually BE saved, provided they persevere in faith and die in God's friendship.
Immaculate Heart of Mary, triumph soon.
Sacred Heart of Jesus, have mercy on us.