In his book The Gospel-Driven Life, Horton addresses how the Gospel in its fullness is materially sufficient for all of life. After addressing the Purpose Driven life paradigm, Horton continues to briefly address the issue of contemplative spirituality, especially as promoted by the Quaker mystic Richard Foster.
Horton starts off by mentioning Foster's disclosure of his "spiritual formation agenda" in "a recent Christianity Today article". In that article, Foster is quoted as lamenting the lack of growth in Christians because "having saved by grace, these people have become paralyzed by it" (p. 146). The suggested solution to such spiritual apathy accordingly is to
... "do all we can to develop the ecclesiola in ecclesia — 'the little church within the church,' " referring to the examples of Lutheran pietism's collegia pietatis, John Wesley's "holy clubs," and the "inner mission" of the Norwegian pietists. As Foster observes, these Protestants movements have their roots in the heritage of Catholic spirituality, identified especially with Francis of Assisi, Theresa of Avila, John of the Cross, and Thomas à Kempis. (cited in p. 146)
Horton states however that he is not going to "tackle the question of spiritual discipline [per se]" here in this book. "Rather, it is to interact with the paradigm of sanctification (the Christian life) as chiefly the imitation of Christ" (p. 147).
Horton starts off by commending Foster's worry about the Antinomianism present in the church and the eclipse of the holiness of God therein. Also,
... Foster is right that there is also a kind of "cheap grace" that fulfils the fond dreams of the antinomian who comforts himself with the syllogism: "God likes to forgive, I like to sin: what a great relationship!" Even if we eschew antinomianism, there is a kind of laziness that does not revel equally in the "already" of new life in Christ and the "not yet" of its consummation. (p. 147)
That having being said, Horton tackles the fundamental errors of the "spiritual formation agenda" in its view of the Christian life: namely confusing works and grace, and justification and sanctification (thus committing the same error as Rome).
But I'm [Horton] not sure how directing people to greater concentration on themselves is going to overcome the narcissistic captivity of our times. As Thomas Finer has documented in A Contemporary Anabaptist Theology, the Anabaptists — whose leaders were trained by the Brethren of the Common Life [of which Thomas à Kempis was formative in its development] — were no more interested in the justification of the ungodly than Rome. The whole emphasis was on discipleship, defined as the imitation of Christ.
The Spiritual Exercises of Ignatius of Loyola are of a similar orientation. Ignatius founded the Jesuit order for the express purpose of opposing the Reformation. Through not without occasional praise, Luther saw his experience with the Brethren of the Common Life as encouraging a theology of glory: ascending to God through works and mysticism. Calvin looked upon his schooling at the ascetic Collège de Montaigu as "servile labor" under the burden of severe regulations and no gospel, while Ignatius recalled fondly his time there as a student. (pp. 147-148)
We can notice the contrast that is already in the process of forming. The "spiritual formation agenda" has its roots in Catholic pietistic mysticism with its emphasis on "discipleship" so-called, and is a "theology of glory" being focused with trying to bring themselves up to Christ and God by their own works of piety, instead of the Reformational emphasis on Justification by grace alone through faith alone, apart from works.
Horton continues to differentiate the counterfeit "spiritual disciplines" from the biblical "means of grace" as follows:
It is striking ... that Luther, Calvin, and other reformers — many of whom (like Luther himself) were former monks — did not throw out the baby out with the bathwater. Sharply critical of using monastic rituals to ascend a ladder to God, they nevertheless held private as well as public prayer in the highest possible estimation. Luther thought that the busier he was in a given day, the more he needed to prepare for it through earnest prayer and reading of Scripture. The Puritans not only wrote sermons and doctrinal treatises, but devotional guides, meditations, and books of prayers. ...
The issue is not whether we engage in personal disciplines or habits of meditative prayer and reading of Scripture, but whether we do so in a gospel-driven manner. Is it a technique for personal transformation or is it a saving and sanctifying encounter with the Triune God who has met us in his incarnate Son? Are we working toward our justification or from it? Are we being drawn to look outside of ourselves, to Christ, or are we feeding our natural tendency to focus on ourselves and our inner life? Obviously, if the significance of Jesus Christ lies principally in his offering a moral example, faith in Christ is not absolutely necessary. ... We do not need an incarnate, righteousness fulfilling, curse-bearing, resurrected Savior if salvation comes by imitation. (pp. 148-149. Bold added)
The difference between the sanctification paradigm of Foster and those who promote Contemplative Spirituality (CS) on the one side, and the Reformation paradigm on the other, is that between life and death; light and darkness; Salvation and Damnation. The CS paradigm brings one back under the Law in working for one's salvation, and thus denies the true biblical Gospel which alone saved. Contemplative Spirituality therefore is soul-damning and potentially brings its adherents (and most definitely its recalcitrant proponents) under the anathema of God (Gal. 1:8-9)!
... Augustinians recognized that defining salvation or the Christian life as the imitation of Christ (imitatio Christi) presupposes a woefully inadequate doctrine of sin and therefore of God's saving grace in Christ.
... the reformers recognized that grace is first and foremost God's favor toward sinners on account of Christ. This "justice" or "righteousness" by which we stand accepted in God's presence is imputed, not infused; declared immediately, not progressively recognized. At the same time, they just as strongly affirmed that God's Word does what it says. Everyone whom God declares to be righteous is also progressively sanctified. (p. 149)
... Nowhere in this lodestar passage [Rom. 7] for the Christian life does Paul direct our attention to the imitation of Christ. He has already painted too dark (realistic) a picture of human depravity to imagine that the devil, the world, and our sinful hearts could meet their match in our deeper commitment to follow Christ's example. ... He calls us not simply to imitate Christ but to be crucified, buried, and raised with him. ... But before he speaks an imperative, he announces the indicative of the gospel: Christ's saving work has accomplished far more than we imagined. (p. 150)
The CS paradigm is based upon a Pelagian or semi-Pelagian view of Man which trivializes the doctrine of the sinfulness of Man, while the biblical paradigm acknowledges the Total Depravity and Sinfulness of Man.
The "imitation of Christ" paradigm of spirituality makes Christ's self-sacrifice and humility an analogy for our discipleship. The "union with Christ" paradigm makes our love and service an analogy of Christ's inimitable accomplishment. Being in Christ is the perpetual source of our becoming like Christ, not vice versa (p. 152)
Apart from the imputation of righteousness, sanctification is simply another religious self-improvement program determined by the powers of this age (the flesh) rather than of the age to come (the Spirit). (p. 153)
The CS paradigm reverses the order of the indicative and the imperative, and therefore is purely of Man, therefore it is repugnant to God.
In conclusion, the entire thrust of Contemplative Spirituality is one of works righteousness. It attempts by its own strength to climb up to God, and thus it is contrary to the Gospel. Contemplative Spirituality is anti-Reformation and anti-God, and thus not to be practised by Christians.