Does eternal security mean Christians can do whatever they want?
No. Eternal security is not license to sin. Scripture does not teach that because believers are safe and secure they are free to do whatever they want. Believers live in constant awareness, not wanting to fall or sin, while knowing they could, and true children of God are convicted and seek forgiveness.
Les teaches that eternal security does not mean Christians can do whatever they want. He says the first accusation people make is that if they can never be lost, they will tell people they can do whatever they want. He answers, "Never!" and insists, "grace is not license." He warns not to get the idea that because we are safe and secure, we are free to do what we want. Instead, believers live in constant awareness that they do not want to fall or commit sin, but are commonsensical enough to know they could. He hopes never to fall into great sin, though all are guilty of mundane sins and thoughts. He uses David as an example: David was a believer, fell into sin, but did not lose his salvation. David begged for forgiveness, and Les says this was because David was a true child of God; otherwise it never would have bothered him.