Sola Gratia, or Grace Alone, is the third Sola of the Reformation. It teaches that salvation comes through grace alone and is no way merited by the sinner.
According to the Catholic process of salvation, God cleanses man’s sin through the sacrament of Baptism. Through the sacrament of Baptism the ability to live righteously has been "infused." Man has been spiritually altered so that he is enabled to live a righteous life and inherit eternal life. Thus, a Catholic must purify himself of all the stains of past sins as well as all post baptism sins. In doing so, He will make himself like Christ and able to stand in the presence of God. Once he attains this righteousness (whether it’s here or in purgatory), man has the ability to enter the kingdom of God.
While the Catholic seeks to become conformed to Christ (through God’s grace) he must be vigilant to confess all mortal sin. Failure to do so will lead to eternal condemnation.
Ultimately, the Catholic has to work out his salvation on two fronts. Even though he is guaranteed heaven if he does not commit a mortal sin, he still has to cleanse himself of the stain of sin through God assisted merit and purging in purgatory. Secondly, the saving graces are applied through baptism and confession. If these sacraments are not administered, he should request to be buried in an asbestos swimsuit.
All this goes to show you that while they view salvation as a gift, it is a gift in the sense that God helps you help yourself. They may believe in grace, but grace is a necessary condition and not a sufficient one.
Let me explain. A logic textbook will teach you that a necessary condition is a circumstance which must be present for the assertion to be true; however, the presence of the circumstance does not automatically make the condition true. For instance, clouds are a necessary condition for rain. It is impossible to have rain without clouds, but there are many times when we have clouds without rain. Another example would be that having four sides is a necessary condition for a square.
In contrast a sufficient condition is one which, if satisfied, automatically assures the statement’s truth. So rain is a sufficient condition for clouds. If rain is present, then there must be clouds. Or conversely, being a square is sufficient for having four sides.
For the Catholic, grace is a necessary condition for salvation. You cannot have salvation without it. However, it is not a sufficient condition, as man must work to complete the job.
In contrast, the Bible teaches that grace is a sufficient condition. God gives us the faith so that we may repent and believe(Eph. 2:8-9). Thus, God applies the substitutionary death to our account and we are justified before God. During this transaction Christ also imputes His own righteousness to us (Rom. 4:5; 2 Cor. 5:21). Consequently we stand before the court of God completely justified. God's grace is not a necessary condition, but a sufficient condition for our salvation. Where there is grace given to the sinner, there is certain salvation. Thus we agree with the Reformers that we are saved by grace alone!