In his commentary on the Lord’s Prayer, Thomas Watson has a great discussion of the preservation of the saints (a.k.a. the “P” in TULIP or the last part of the Canons of Dort). He says “a saint’s perseverance is built upon three immutable pillars.”
1) Upon God’s eternal love. We are inconstant in our love to God; but he is not so in his love to us. ‘I have loved thee with an everlasting love;’ with a love of eternity (Jer. 31.3). When once the sunshine of God’s electing love is risen upon the soul, it never sets finally.
2) Upon the covenant of grace. It is a firm, impregnable covenant; as you read in [2 Sam. 23.5] ‘God hath made with me an everlasting covenant, ordered in all things and sure.’ This covenant is inviolable, it cannot be broken; indeed, sin may break the peace of the covenant, but it cannot break the bond of the covenant.
3) Upon the mystical union. Believers are incorporated into Christ, they are knit to him as members of the head, by the nerve and ligament of faith, so that they cannot be broken off (Eph. 5.23). As it is impossible to sever the yeast and the dough when they are once mingled, so it is impossible when Christ and believers are united to be separated, even by the power of death or hell .
Well said; reminds me of the answer of the Westminster Larger Catechism that has to do with the perseverance of the saints (Q/A 79). I’ve put the numbers in the text to more clearly show the reasons saints are preserved:
“True believers, by reason of the 1) unchangeable love of God,
and 2) his decree
and 3) covenant to give them perseverance,
4) their inseparable union with Christ,
5) his continual intercession for them,
and 6) the Spirit and seed of God abiding in them,
can neither totally nor finally fall away from the state of grace,
but are kept by the power of God through faith unto salvation.”
The above quotes by Thomas Watson, which I edited slightly, are found on pages 131-132 of The Lord’s Prayer.