how small and gradual are the steps by which men may go down into great sins

The various steps in Peter's fall are clearly marked out by the Gospel-writers [Luke 22:54–62]. They ought always to be observed in reading this part of the apostle's history. The first step was proud self-confidence. Though all men denied Christ, yet he never would! He was ready to go with Him both to prison and to death! The second step was indolent neglect of prayer. When his Master told him to pray, lest he should enter into temptation, he gave way to drowsiness, and was found asleep. The third step was vacillating indecision. When the enemies of Christ came upon Him, Peter first fought, then ran away, then turned again, and finally "followed afar off." The fourth step was mingling with bad company. He went into the high priest's house and sat among the servants by the fire, trying to conceal his religion, and hearing and seeing all manner of evil. The fifth and last step was the natural consequence of the preceding four. He was overwhelmed with fear when suddenly charged with being a disciple. The snare was round his neck. He could not escape. He plunged deeper into error than ever. He denied his blessed Master three times. The mischief, be it remembered, had been done before. The denial was only the disease coming to a head.

Let us beware of the beginnings of backsliding, however small. We never know what we may come to, if we once leave the king's high-way. The professing Christian who begins to say of any sin or evil habit, "it is but a little one," is in imminent danger. He is sowing seeds in his heart, which will one day spring up and bear bitter fruit. It is a homely saying, that "if men take care of the pence the pounds will take care of themselves." We may borrow a good spiritual lesson from the saying. The Christian who keeps his heart diligently in little things shall be kept from great falls.

—J.C. Ryle, 'Expository Thoughts on Luke'