Be watchful, stand firm in the faith, act like men, be strong. (1 Corinthians 16:13)
There are two general battlefronts that we must watch: there is the battlefront within, and the battlefront around us.
First, let’s talk about the battlefront within. This is perhaps the most important. If I am not watchful over my own heart, and I fall into sin in some way, others are affected - the church, my family, and society.
Being watchful over our own hearts requires first and foremost that we understand that our hearts are sick.
Jeremiah 17:9 - The heart is deceitful above all things, and desperately sick; who can understand it?
Mark 7:21–23 - For from within, out of the heart of man, come evil thoughts, sexual immorality, theft, murder, adultery, coveting, wickedness, deceit, sensuality, envy, slander, pride, foolishness. All these evil things come from within, and they defile a person.”
Granted - when we are converted to faith in Christ - we are given a new heart.
Ezekiel 36:26–27 - And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh. And I will put my Spirit within you, and cause you to walk in my statutes and be careful to obey my rules.
But understand that your old heart - the one that is sick is still in you and is at war with your new heart, which is why Paul says…
Romans 7:22–23 - For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members.
This is why we must be watchful - there is war going on within every Christian. If there is not a war, then you may not be truly converted.
Being watchful requires introspection through the Word and through prayer. David explains it best:
Psalm 139:23–24 - Search me, O God, and know my heart! Try me and know my thoughts! And see if there be any grievous way in me, and lead me in the way everlasting!
What this shows us is how impossible it is to watch our own hearts apart from the soul-piercing gaze of the Holy Spirit who alone can illuminate the depths of our our hearts and show us what’s in it.
The better we know our own sick hearts, the more effective our watching will be - for we will be keenly aware of how deceitful and conniving our old hearts can be. We know that our old heart lies to us about many things, and seeks to justify all sorts of behaviors, attitudes and motives. We know when our heart is lying to us, when it is trying to allure us away from the truth and getting us to believe lies. We are on guard against those attempts - we know the kind of tricks the heart likes to pull to get us to do what it wants us to do.
Being watchful involves regularly questioning our motives, desires, attitudes and inclinations. And it also involves strengthening our new heart created in us by the Holy Spirit through regular communion with God through prayer, the Word, fellowship and the sacraments.
So I encourage you to make it a regular habit of asking what David asked in Psalm 139 - search me and know my heart. Show me if there is any grievous way in me.