This paper develops the concept of 'spiritual capital' as an analytical lens for a critical assessment of the United Nations 2030 Agenda's approach to inequalities, highlighting both its achievements and its conceptual limits. As the 2030 horizon approaches, it has become increasingly clear that the SDG framework, while robust in its institutional and material dimensions, leaves important aspects unaddressed. The paper argues that one of these is the absence of spirituality as a constitutive element of sustainability and as a resource for addressing inequalities. Rooted in ethical values and the wisdom of diverse traditions, spiritual capital fosters purpose, resilience, and a sense of belonging, among other foundational conditions on which inclusive and sustainable development can flourish. In response, the paper proposes integrating spiritual capital into the SDG architecture in a way that is consistent with its existing logic of goals, targets, and indicators. Specifically, it introduces the idea of a "Goal 0," capable of integrating spiritual capital across all SDGs: rather than adding a further objective, this approach reframes spiritual capital as a cross-cutting principle that can orient sustainability policies. This paper is the result of a collaborative effort with a research group working on the theme of spiritual capital within the context of The Economy of Francesco.