This day the LORD will deliver you into my hand...that all this assembly may know that the LORD saves not with sword and spear. For the battle is the LORD's, and he will give you into our hand. (1Sam 17:46-47)
The LORD your God will save you. He has saved you, right? And "not with sword and spear" but by the blood of King Jesus.
God defeats the Philistines with: a) a young, untested, shepherd, b) slingshot technology, and c) fear in the hearts of the Philistines. At the end of v. 51 the Philistines are defeated: "When the Philistines saw that their champion was dead, they fled."
So what should the Israelites do? Start celebrating? Yes. Turn around and head home? No. But rather, what God delivered, go receive: "And the men of Israel and Judah rose with a shout and pursued the Philistines." (1Sa 17:52)
God saves without swords and spears. He saves as a gift; it's all grace. So receive it. How? Receive it with your sword and spear. The victory God gave Israel over the Philistines was RECEIVED by the Israelites rising up and pursuing the Philistines.
God has saved us by Jesus. Salvation is done: "it is finished." And God has given this to us as a free gift. All we do is receive it.
So receive it, already! Don't turn, head home, put your feet up and binge watch Philistine-blooper vids. Take up the pointy-tipped "means of grace." These are things which God has ordained to be the channels by which His saving-grace gets delivered to the nooks and crannies of our lives.
Embrace disciplines! Build habits! Eat your greens! Do your daily march!
Take the swords and spears of grace and receive into your hands the Lord's victory-gift. It's all grace. Grace must be received.
God has done everything that needs to be done, don't mistake my meaning. But in God's kindness He shares this joy with us: that we might enter, now that salvation is accomplished, the application of that salvation to our lives and worlds. God's great joy is being glorified for what Christ has done. He invites us to share His joy by reveling ourselves in what Christ has done. Get this joy, God's joy. Get to know your Spirit-given swords and spears. Introduce them to the Philistine-presences in your heart and mind.