One of the mistakes we Christians make is to close our mind against the conviction of the Holy Spirit, assuming that it is an accusation or doubt coming from the Devil. It is the knowledge of the 'truth' or reality that can set us free from all the corruption that is there is our flesh (Jn.8:32) because of which we are so very unlike Christ. When truth comes, it exposes the actual situation in our life. Even though it is painful for us to face it, that is the first step we have to take towards being set free. What happens when we close our mind to such painful realities is that we remain at the same spiritual level or even backslide, while at the same time assuming that we are doing fine.
Think of what happens when a man who is not born again assumes that he is a child of God because of some false assurances. Now and then he comes across things that wake up his conscience and alert him to realise he needs to be born again. But then he tells himself that he is a child of God by remembering some past event and also misquoting verses that do not really apply to him. On the contrary, if only he would examine himself based on the word of God – has his direction of life changed towards God now, does he now have a hatred towards all sin, is he in a battle to stop sinning with constant cries to God for help, are his thinking and practical life getting more and more like Christ? If the answers are 'yes', then he can be assured of his salvation.
"God has not given us a spirit of timidity, but of power and love and discipline" (2Ti.1:7). 'Sound mind' as in the KJV can be translated as 'discipline' and 'self-control' also. This is what God has planned for us. But don't we need to see if we are actually experiencing these in practical ways? Or should we close our mind and 'claim' that these are so? Some people take 'sound mind' to imply that Christians cannot have mental illnesses! When they become ill, they refuse to treat it, as they would have done for other physical illnesses, but keep claiming that have a sound mind!
There may be many doctrines where others disagree with us. Isn't it necessary to examine their teachings before coming to conclusions? Or do we simply assume we are right and stay put with our doctrines without questioning them?
There is a place to close our mind towards the Devil's attacks. For example, after we have forgiven someone and the thoughts of what he has done keep coming back, we have to refuse to entertain those thoughts further, saying we have already forgiven him. If we have actually experienced being born again and that has changed our life entirely, we shouldn't waste any more time going over that question again.
The Devil knows whom to trouble with doubts and whom to soothe with false assurances. Our safety comes from being honest before God and being willing to receive whatever He tells us and then to do it. Then we are not 'insecure' and can deal with challenges without wavering.