[1- Roman Catholic Council of Trent: Sess Vi, Canon 23: "If anyone maintain that a man once justified can not lose grace, and, therefore, that he who falls and sin never was truly justified, let him be accursed." ]
The Westminster Confession (Reformed) makes the following points:
1) Assurance of salvation is possible for those who believe.
2) This is based on the promises of scripture and is not a conjecture.
3) You can have faith but not have assurance.
4) True believers may have their assurance shaken.