What basis should be applied when discussing a constitution? Citizenship features in the US constitution, but it isn't part of the unwritten constitution of NZ. Sovereignty is another basis, but sometimes political supremacy is called sovereignty so it's important to know what the essential qualities of sovereignty are. Humanity is another basis, but humanism suffers from the same problem as citizenship, that these forms of society are unable to gain independence and remain weak and vulnerable. Rationality is another approach, but it doesn't have the heart of a king.
Forming a coherent philosophy that can be used as a basis for a constitution involves considering the transient nature of society, not just for individual members but for society as a whole. The Treaty of Waitangi highlights NZ's origins as a society but also illustrates how agreements involving protection typically result in the dominance of a single party. The transience of monarchy is illustrated by the Norman conquest and by the Magna Carta.
NZ's national anthem illustrates the historical role of religion, but there is an increasing awareness of the problem of conflicting religious beliefs. Perhaps the best course is to retain the theism of NZ's unwritten constitution but show no favouritism to any particular creed.