The heart is deceitful above all things and beyond cure. Who can understand it? ---Jeremiah 17 vs 9
The spirit of a sound mind does not mean just going by what we or others think or feel is reasonable or expedient. Our imperfect mind and heart can be like a watch that is going either too fast or too slow. Being guarded by it could bring us serious trouble. We need to calibrate our mind and heart by God's reliable standards. With good reason the Bible admonishes us "Trust in God with all your heart and do not lean upon your own understanding. In all your ways take notice of him and he will make your part straight." (proverb 3 vs 5&6 ) Note the expression "do not learn on your own understanding." it is followed by "take notice of him [God]." He is the one with a truly sound mind. Thus, it follows that whenever we are faced with a decision, we need to turn to the Bible to see what God's view is. Then we should base our decision on it. That is using the spirit of a sound mind.
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