Commentaries:
Verses 7 and 15 focus on "Today," meaning "right now"—the subject must not be put off. In this way, "Today," injects a sense of urgency as well as the thought of "as long as the opportunity exists," implying that now is our time of salvation. It must not be wasted because God calls one only once.
At the same time, he is suggesting that the Israelites failed because they did not use their faith as a day-to-day function of life. Faith is not something to be held in reserve for the really big trials of life, but it is the solid foundation of daily living. It is this level of faith that Jesus was concerned about when He asked, "When the Son of Man comes, will He really find faith on the earth?" Living faith motivates every thought meant to produce action, beginning with what God requires before all else. Paul is urging believers to work toward using faith in God as the driving force of everything we do each day.
John W. Ritenbaugh
Fully Accepting God's Sovereignty (Part Two)