Hundredfold Reward

This which is here said, shall receive a hundredfold, may be understood in a higher sense. This means, that all who have despised temporal things for the sake of the kingdom of heaven through undoubting faith, taste the joy of the same kingdom in this life which is full of persecutions, and in the expectation of the heavenly country, have a share in the happiness of all the elect.

But because not all accomplish a virtuous course of life with the same zeal as they began it, it is added, "But many that are first shall be last, and the last first;" for we daily see many persons who though they are laymen, are eminent for their meritorious life; but others, who from their youth have been ardent in a spiritual profession, at last wither away in the sloth of ease, and in a lazy foolishness, end in the flesh what they had begun in the Spirit. (Note: This is written by St. Bede the Venerable)

To avoid such a shameful end we must remind ourselves that our life is a battle. In battle, the first thing an enemy does to you once you are captured is disarm you - making you powerless to exercise your will. This is what happens when we fall into sin: although we retain our free will, that will is weakened. With each successive sinful act, we bind ourselves to the temporal world to such an extent that we cannot rule over our lives. That we have to fight constantly to remain free from the chains of sin is why we are known as the Church Militant, members of God's army on Earth. Tomorrow marks the beginning of Lent - the season of discipline. Our enemy: the devil and all the fallen angels and our own sinful nature. Our reward: citizenship in the Kingdom of God. Our weapons: prayer, fasting, almsgiving, and the Sacrament of Penance. Soldiers of Christ - prepare for battle!

參考 References:
Catena Aurea (St. Thomas Aquinas)
On the Gospel of Mark (St. Bede the Venerable)
Quinquagesima Sunday: Prepare for battle!