Because of these remnants of sin dwelling in them and also because of the temptations of the world and Satan, those who have been converted could not remain standing in this grace if left to their own resources. But God is faithful, mercifully strengthening them in the grace once conferred on them and powerfully preserving them in it to the end.
The Canons of Dort, The Fifth Main Point of Doctrine: The Perseverance of the Saints. Article 3- God’s Preservation of the Converted.
