Therefore, since we have been justified by faith, we have peace with God through our Lord Jesus Christ. Through him we have also obtained access by faith into this grace in which we stand, and we rejoice in hope of the glory of God. (Romans 5:1-2 ESV)
Some use Mac OSX. Some are in transition from Windows XP to Windows Vista. A few use Linux. But everyone who has a computer has to have an operating system (OS) to make it work. Without an OS, a computer is just a bulky dust collector. You can have power coming to it. You can tap the keys for hours, but without software to tell the hardware what to do, a computer is just a bad lamp: a lot of electricity for poor illumination.
But with an OS (and the knowledge to use it) the possibilities are practically endless.
In the Kingdom of Heaven, faith is the OS. By faith alone we have access to the amazing possibilities of God available to the believer, just as by the OS we have access to the world wide web, the educational and productive (and entertainment) capabilities of our computers. When God says "...the just shall live by faith." He is telling us to master the OS. Too many of us can't be bothered to become adept at faith. Would you believe someone was getting the best out of their computer if all they ever used it for was to play Solitaire? There's so much more! But we paddle around in the shallows of faith as if it were the deep end of the ocean.
"...we have ACCESS by faith into this grace..." All of God is available to us. All of His ability. All of His power. All of His wisdom. All that we need to turn our world right side up. All that we need to do is access it, and the only access key we have is faith in Him. By His plan, it's the only key we need!
And what more shall I say? For time would fail me to tell of Gideon, Barak, Samson, Jephthah, of David and Samuel and the prophets-- who through faith conquered kingdoms, enforced justice, obtained promises, stopped the mouths of lions, quenched the power of fire, escaped the edge of the sword, were made strong out of weakness, became mighty in war, put foreign armies to flight. (Hebrews 11:32-34 ESV)