"A big fish easily breaks through the same net which holds a little fish captive. The Christian's faith is strong or weak as he finds it easy or hard to break from temptations to sin. When an ordinary temptation entangles you like a fly in a spider's web your faith is very frail. Peter's faith was weak when nothing more than a maid's voice drove him to deny Christ; but it became strong when he withstood and refuted the threats of a whole council (Acts 4:20) . Even when faith does not have a hand to throw down an enemy, it still has a hand to lift up against it and a voice to cry out to heaven for help. True faith finds a way to combat sin.
Christian, compare yourself with yourself. Do lusts snare your heart and lure it away from God as forcefully as they did several months ago? Or can you honestly say your heart is overcoming them? Since you now know more about Christ and have glimpsed His spiritual glories, can you now pass by their door and not look in? And when temptation knocks, can you shut the door in its face? If the power of sin dies, you can be sure your faith is lively and vigorous. The harder the blow, the stronger the arm that gives it. A child cannot deliver such a wound as a man. And while weak faith cannot deliver a fatal blow to sin, strong faith is both willing and able to do this. The more obedience and love in the Christian's walk, the stronger his faith.
Faith works by love, and therefore its strength or weakness can be gauged by the strength or weakness of the love which it activates in a Christian's behavior. The strength of a man's arm that draws a bow is proved by the force in the arrow's flight. And certainly the strength of our faith may be known by the force with which our love mounts to God. It is impossible that weak faith-- which is unable to draw the promise as strong faith can-- should as powerfully impress the heart to love God as stronger faith can."
Quoted material from, ”The Christian in Complete Armour Daily Readings in Spiritual Warfare” by Gurnall and James S Bell. http://www.moodypublishers.com/pub_productDetail.aspx?id=41823&pid=53617