What is The Perseverance of Believers?
The elect are those whom God has accepted in [Christ] the Beloved, effectually called and sanctified by His Spirit, and given the precious faith of His elect. These can neither totally nor finally fall from the state of grace, but they shall certainly persevere in grace to the end and be eternally saved. For God will not repent of His gifts and calling, therefore he continues to bring about and nourish in them faith, repentance, love, joy, hope, and all the graces of the Spirit that lead to immortality.
Many storms and floods may arise and beat against them, yet these things will never be able to sweep them off the foundation and rock upon which they are fastened by faith. Even though unbelief and the temptations of Satan cause the sight and feeling of the light and love of God to be clouded and obscured from them for a time, yet God is still the same and they are sure to be kept by His power until their salvation is complete. Then they will enjoy the purchased possession which is theirs, for they are engraved on the palms of His hands, and their names have been written in the book of life from all eternity.
This perseverance of believers does not depend on their own free will, but on the immutability of the decree of election, which flows from the free and unchangeable love of God the Father. It also rests on the efficacy of the merit and intercession of Jesus Christ and their union with Him, the oath of God, the abiding of His Spirit, the seed of God within them, and the nature of the covenant of grace, from all of which arises also its certainty and infallibility.
They may fall into serious sins through the temptations of Satan and the world, the power of the corruption remaining in them, and neglect of the means for their preservation, and may even continue in them for a time. In this they incur God's displeasure, grieve His Holy Spirit, have their graces and comforts impaired, have their hearts hardened and their consciences wounded, and hurt and offend others, and bring present chastisement upon themselves. Yet they will [in time] renew their repentance and be preserved through faith in Christ Jesus to the end.