Why use the Lam Rim as a path of spiritual development? From my own experience I can give 3 reasons:

1. It is specifically oriented toward a process of spiritual growth, rather than mere memorization of texts or inculcation and recital of beliefs.
2. It is systematic, providing a comprehensive framework for organizing religious precepts (at least, in my experience, those of Christianity and Buddhism).
3. It is cumulative: Each step provides a base of knowledge, practice and motivation upon which the next step can be built.

"Four especially great facets" of the Lam Rim are listed by the Third Dalai Lama^[1] in his work Essence of Refined Gold, cited in the Dalai Lama's Refining Gold:

1. "It reveals how all the various doctrines of the Buddha are non-contradictory."
   This aspect helps in understanding the coherence and unity of Buddha's teachings. For Buddhists, it reinforces the idea that different teachings are parts of a whole, tailored for varied levels of understanding and capacities. Christians and other spiritual seekers can draw parallels with their own traditions, recognizing that diverse teachings and scriptures can coalesce into a unified spiritual path. This encourages a holistic approach to spirituality, where various aspects and teachings complement rather than contradict each other.
2. "All the various teachings will be taken as personal advice."
   This facet emphasizes the practical application of teachings. For Buddhists, it means integrating the Dharma into daily life, not just as philosophical concepts but as lived experiences. Christians and other spiritual seekers can similarly approach their sacred texts and teachings as personal guidance, aiming to live the values they teach. This personalization of spiritual teachings fosters a deeper, experiential understanding of one's spiritual path.
3. "The thought of Buddha will be easily found."
   This implies accessibility and relatability of the teachings. Buddhists find this beneficial as it makes the profound wisdom of the Buddha more approachable. For Christians and others, it suggests that the core truths of compassion, wisdom, and interdependence, as taught by Buddha, are universal and can be appreciated within their own frameworks. It allows for an appreciation of the shared human quest for understanding and compassion across different faiths.
4. "The great mistake of abandoning a lineage of Dharma will spontaneously be arrested."
   This aspect highlights the importance of respecting and preserving the continuity of spiritual teachings. For Buddhists, it underscores the value of lineage and the transmission of teachings. For Christians and other spiritual seekers, this can be seen as an encouragement to value and uphold the integrity of their own spiritual traditions and teachings. It speaks to the importance of maintaining a connection to one’s spiritual heritage and learning from the wisdom of past masters and teachers.

These facets of the Lam Rim offer a framework for understanding and applying spiritual teachings in a way that is coherent, personal, accessible, and respectful of tradition. They encourage an integrative approach to spirituality, where different teachings and practices are seen as complementary, allowing individuals from various faiths to deepen their understanding and practice in a way that is harmonious with their own beliefs and traditions.

[1] The original source of these "Four especially great facets" appears to be Verse 7 of Tsongkhapa's Lines of Experience.