“He [Jesus] upholds the universe by the word of his power” (Hebrews 1:3).
We are very used to thinking of creation as a single event, something which happened at a single point of time. This is not the view of Bible. Rather than creation being a single, finished event it is understood as something which is ongoing. God creates the heavens and the earth, and he continues to sustain it. No idea of making something, setting it going and then leaving it alone. Rather the idea is that the God who is being continues to keep things in existence though the life which he gives.
In this passage, Christ is identified as the one who sustains the universe. There is a logic here: if creation was spoken into being with a “let there be...” (Genesis 1), and if Jesus is the Word of God (John 1), then it follows that Jesus is the one through whom everything came into being. As the Apostle Paul puts it: “For by him all things were created, in heaven and on earth, visible and invisible” (Colossians 1:16). More: in Acts 3:15, Jesus is referred to as the “Author of Life”.
Life not only came from God, but continues to come from God. This is the way in which Christ “upholds” the universe, and This act of upholding serves to underline our entire dependence upon God. We not only owe him our existence, but also our continuing existence. As life flows back into the countryside in Spring, it flows from God. As life ebbs from the body at death, it continues in eternity before God.