A substitute is someone who takes the place of or acts instead of another. In education substitute teachers stand before a class usually taught by someone else. In the game of baseball a substitute hitter or runner is commonly used to take another player's place. Even the prime minister, if necessary, appoints a substitute and gives him or her the full authority of leadership.
What is true in the classroom, sports, and politics is also true in our relationship with the living God. We, as sinners, need someone to take our place and act in our stead. Otherwise, we cannot stand before the holy, righteous, and glorious Lord. Today, we shall meet our substitute, the one who “Himself bore our sins in His body” (1 Peter 2:24), who “though He was rich, yet for [our] sake[s], He became poor” (2 Corinthians 8:9).