I believe its helpful to DIFFERENTIATE between Once saved alwas saved and perseverance of the saints!
Because in TODAY's christianity, OSAS means repeat this prayer after me and live as you please.
Whereas perseverance of the saints is FAITH and REPENTANCE, walking in newness of life, a new creature, a changed life and the SAINTS (the ones redeemed by the blood of Jesus) WILL persevere, because its God working in them.
Thats the difference.