Penetration Testing is the most efficient approach to evaluate how secure your IT infrastructure is. This is done by safely attempting to exploit system vulnerabilities, including OS, network, service and application flaws, improper configurations, and even risky end-user behavior.
Compared with a Vulnerability Assessment (which is part of any Penetration Test), this approach will remove any false-positive results and the mitigation process will be simplified from a technical perspective and from the resource point of view.
Information Security Management focuses on preserving the integrity, accessibility, and confidentiality of your data and the IT infrastructure it flows through.
Security Management involves all the processes, workflows, and tools needed to make that happen.
Penetration Testing feeds your Security Management program with independently vetted security priorities you need to address and periodically checks for potential issues that could lead to compromise.
The two approaches are very different but extremely complementary, enhancing each other to improve the performance of your organizational security program.