Why did God decide to save us through faith? (John Piper)

"The salvation from sin and death and judgment that Christ brings is received by faith. Paul illustrates this faith with the case of Abraham in Romans 4:20 and shows how it relates to the glory of God: "No distrust made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God [literally, giving glory to God]." In other words, one reason that faith is the way God saves us is that faith gives glory to God. That is, faith calls attention to and magnifies the glory of God. Faith puts us in the position of weak and dependent and puts God in the position of strong and independent and merciful. So faith is essential to displaying the glory of God."