As a young boy, my family went camping for our summer vacation. One of my favorite parts of camping was the evening campfire. We would begin at dusk and the fire would become brighter as the night sky became darker. Later, I would make my final trek to the bathrooms. To light my way, I'd take a flashlight with me. I'd push the button and have instant light!
How did this light come to be? We might say that it appeared when I pushed the button, that I caused it to happen. That is only part of the story. The bigger picture is that my action, combined with the support system of the batteries and the internal components of the flashlight, caused the light to appear. It was the entire system, and my action, which brought forth light. Without my action, nothing. Likewise, without batteries or a working bulb, nothing.
When the psalmist says, "Your word is a lamp to my feet," he means that God's word guides him. We might ask how this happens. Like with the example of the flashlight, it is not by picking out "the rules" of the Bible and attempting to diligently follow them that we find guidance from God. It is not one component only. This is like trying to turn a flashlight on that has no batteries. We need the whole "support system" of the Bible to see God's guidance for us.
The word of God is not a light for our path when we look for rules or checklists, but when we understand the entire story--God's plan of redemption and the gospel. When we understand the Bible in this framework, and combine that understanding with our actions, it is then that the Bible becomes a guide, leading us closer to God.
Later in the psalm the writer says, "The sum of your word is truth, and every one of your righteous rules endures forever" (119:160). When we understand the "rules" within the "sum" of the gospel, when we see how everything is connected to Christ and the gospel, then God's word transforms and changes us.
This is why the psalmists encourage us to meditate on God's word. Read it, get to know it, not as individual rules, but as God's story of redemption through the gospel in Jesus Christ. Then our actions become part of the "sum total" of God's story, for God's glory.