I know that Pelagian was the source of a heresy, but could you give details of the Pelagian view of justification?
According to Pelagius, therefore, a man was able to justify himself by performing good works that were pleasing to God. We see this error in Rome's emphasis on a works-based salvation and on its sacramentalism. This error, sadly, has now filtered into many Protestant churches who preach a semi-Pelagianism by maintaining that men are responsible for their own salvation through their own piety which compels them to "accept" Christ as their Savior. Election according to God's will is thus effectively nullified and made wholly dependent upon men and not God from start to finish.
Thanks to the Reformation, the church and its members were reminded that no man can do anything God-pleasing unless that man has been born again by the Holy Spirit, according to the will of God.
"For it is God which worketh in you both to will and to do of his good pleasure." -- Phil. 2:13"Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost" -- Titus 3:5
Building upon Augustine, the Reformers returned to the Biblical definition of justification as a once-for-all, never-to-be-repeated act in which God declares the guilty sinner to be righteous, not because God has gradually made him righteous by infusing grace into him, but because God has declared him to be righteous because of the righteousness of Christ imputed to him.
It is such a profound distinction. Paul understood the difference when he asserted that no man is righteous and all men sin all the time, but mercifully, God does not hold us accountable for our sins. He holds Christ accountable for our sins, and by Christ's sacrifice for those sins, we have been forgiven.
And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins: But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God; From henceforth expecting till his enemies be made his footstool. For by one offering he hath perfected for ever them that are sanctified. Whereof the Holy Ghost also is a witness to us: for after that he had said before, This is the covenant that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them; And their sins and iniquities will I remember no more. Now where remission of these is, there is no more offering for sin." -- Hebrews 10:10-18"By the which will we are sanctified through the offering of the body of Jesus Christ once for all.
Christ's righteousness is what saves the fallen sinner, and not our own. This righteousness is freely imputed to whom God will have mercy upon, determined by God from before the foundation of the world. God leaves nothing to "chance," since "chance" is as non-existent as men's own righteousness.
For who hath known the mind of the Lord, that he may instruct him? But we have the mind of Christ." -- 1 Corinthians 2:12,16"Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God...
All a gift, all by grace.