The best description of the purpose of performing security certification is to formalize the confirmation of compliance to security policies and standards. Security certification is the process of evaluating and validating the security posture and compliance of a system or network against a set of predefined criteria, such as security policies, standards, regulations, or best practices. Security certification results in a formal statement or document that attests the level of security and compliance achieved by the system or network.

A. To identify system threats, vulnerabilities, and acceptable level of risk is not the best description of the purpose of performing security certification, but rather the purpose of performing security assessment. Security assessment is the process of identifying and analyzing the security threats, vulnerabilities, and risks of a system or network, and determining the acceptable level of risk and the risk mitigation strategies.

C. To formalize the confirmation of completed risk mitigation and risk analysis is not the best description of the purpose of performing security certification, but rather the purpose of performing security accreditation. Security accreditation is the process of authorizing and approving the operation of a system or network based on the results of security certification and risk analysis, and the acceptance of residual risk.

D. To verify that system architecture and interconnections with other systems are effectively implemented is not the best description of the purpose of performing security certification, but rather one of the possible aspects or objectives of security certification. Security certification can cover various aspects of system security, such as architecture, design, implementation, configuration, operation, maintenance, or interconnection.

References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 3, page 147; Official (ISC)2 CISSP CBK Reference, Fifth Edition, Chapter 3, page 123