The four principal functions of the Central Bank of Nigeria under its enabling Act are:

1. Issuance of legal tender currency in Nigeria.
2. Maintenance of external reserves to safeguard the international value of the Naira.
3. Promotion of monetary stability and sound financial systems.
4. Acting as a banker and financial adviser to the federal government.

Explanation:
The Central Bank of Nigeria plays a vital role in regulating the country’s financial stability through its statutory functions, including currency issuance, managing reserves, maintaining monetary stability, and advising the government on financial policies.