Here is the context of the conversation:
Then he said to his disciples, "Let us go back to Judea."
"But Rabbi," they said, "a short while ago the Jews tried to stone you, and yet you are going back there?" (John 11:7-8)Jesus' statement above came in answer to this.
Jesus wasn't afraid of being stoned
So Jesus was pretty nonchalant about the risk of his being stoned. He obviously was not afraid. Why wasn't he afraid?
For one, he was completely dependent upon the Supreme Being. He relied on God. He trusted God: This means to completely rely on God and God's protection.
The second reason that Jesus was serving the Supreme Being. He was trying to give people information that would help them re-develop their love for God. Jesus didn't come to die on the cross, as many try to portray. He came to teach us that if we love and serve God, we will be fulfilled.
This text illustrates just how important that mission was to Jesus - that he was prepared to return to a place where the Jews had just threatened to stone him in order to keep teaching his students, including Lazarus whose body was dying.
Furthermore, Jesus' answer to his disciples also illustrated his intent to please God, and teach his students.
What does Jesus mean by not stumbling?
This is a simple correlation between walking and life itself. To "stumble" here means to fall away from one's relationship with the Supreme Being. And to "walk by day" means to accept God's guidance and progress through life in a way that is pleasing to the Supreme Being.
This means remembering God, glorifying God and working to do God's will. This is just what Jesus was showing us how to do, by example. He told us to do this and showed us how to do this.
To have "no light" here means to move through life in a way that is not pleasing to the Supreme Being. This means being selfishly motivated. This means trying to use life for our own purposes - trying to enjoy life in a self-centered fashion.
Self-centeredness drives the physical world
This is the primary purpose for most of us in the physical world. Why? Because this physical world is where the self-centered beings are sent - where we take on these temporary physical bodies in order to play out our self-centeredness.
As for those who teach that we need to "love ourselves before we can love others," they are simply deceiving us and telling us what we want to hear so we will follow them. They are taking us further away from our relationship with the Supreme Being.
These teachers say guilt is bad. They say that we need to build our self-esteem, so we should go out and enjoy life to its fullest, and learn to "love ourselves." This is the epitome of self-centeredness. This is an example of what Jesus was talking about: stumbling in the darkness.
Guilt is a message from deep within - a subtle reminder echoing from a distant communication from the Supreme Being trying to remind us of our real nature - our spiritual nature. Guilt is not a bad thing. Guilt is not something we should see as a roadblock to happiness. Guilt is a doorway. It is like being in the total darkness, and then seeing a small light in the distance. If we follow that light, as we get closer, we can start to see by that light.
Our true self is not selfish.
Deep within, our true self is loving and caring by nature. Each of us essentially seeks to return to our pure state of loving and caring, but our self-centered interests interfere with this.
The problem is that we cannot separate our loving and caring nature from our relationship with the Supreme Being. They are interconnected. So as long as we reject or ignore our relationship with God, we will remain essentially self-centered.
One might say they are not self-centered because they care about their family members. But this is also self-centered because they are based on bodily identification. We only care about our family because it is linked to our physical body.
God is the Soul Mate we are always looking for. He is that perfect person we always look for that we think will complete us. When we reconnect with our relationship with God, we also reconnect with our true nature, which is not self-centered. That true nature loves God and loves everyone despite the body they may be wearing at that moment.
God is not some vague force, burning bush or booming voice. God is a Person. He is our dear-most Friend. The problem is that at some point we decided we'd rather be the center of attention than have our Best Friend as the center of our attention.
So we left the spiritual dimension to pursue our ideas for self-centered enjoyment. The problem is, we can never find fulfillment in this chase. We are like fish out of water without our Best Friend. We are like butterflies with no wings without our intimate relationship with God.
We are incomplete without serving and caring for the One who understands us completely, gives us full protection and complete fulfillment. When we care for God (and likewise, His children), we are completing our nature.
Jesus is comparing returning to our lost relationship with the Supreme Being to walking in the daylight. He is comparing stumbling in the darkness to having forgotten the relationship with God that will fulfill us. This is why Jesus' most important instruction was:
"'Love the Lord your God with all your heart and with all your soul and with all your mind.' This is the first and greatest commandment." (Matt. 22:37-38)