The apostle shows how righteousness acts to be protective of the heart or affections in a saved person – a large target of the devil. Here is how self-denial, love for Christ and obedience to the commandments garrison the heart from pollution and shame.
The foundational piece of the Christian’s armour is firstly objective truth – the unchanging doctrines of the faith. (The sword, later, is Scripture used ‘offensively’ to make Christ known). Secondly, the belt is also subjective truth, truthfulness and sincerity for which here are helpful rules.
This foundation of the armour of the believer must be reinforced constantly by a set of simple steps and aims, so that the rich fruits of sincerity – here named – may flourish. And as the armour is taken, God gives the enabling strength.