On the eve of facing the crucifixion, the first three Gospels all recorded how the Lord prayed three times in the Garden of Gethsemane, how sad and mourned (Matthew 26:37-38; Mark 14:33-34; Luke 22:44); only this book records that the Lord still had spare energy to comfort His disciples. This is because He is the "Son of God" in the Gospel of John, which is different from the "Son of Man" in the first three books. However, the Lord was weak in human nature; how transcendent He was in divinity! Here, Christ was clearly encouraging faith in God and in Himself in the face of impending events. Therefore, Jesus reassured them, reminding them that the truth had been revealed and that He had all things in hand.
After being subjected to a battery of cruel treatment, the One they loved was to be brutally removed from the disciples. Their hopes were seemingly dashed to the ground, and they did not know what to do or who to turn to. In perplexed pain and confusion, the disciples approached Calvary. They had to witness His unjust arrest, unlawful trial, and cruel crucifixion. Therefore, the message Jesus gave to them was not only to let their hearts not be troubled but also to give them tools to keep them from worry and fear, which all came back to faith, for if you believe in God, also believe in me. 
Today's world is filled with stress and strain. While we cannot prevent the pressures of life, the Lord Jesus Christ Himself provides us with assurance. The kingdom of Jesus would soon be established on earth. It will be a glorious day when Jesus comes in the clouds to take us to be with Him. Thus, do not let your heart be troubled, and always have faith in God.

Dear Heavenly Father, thank You for the wonderful words of comfort that Christ sent to me. Thank You for sending the Son of God to earth to bring comfort to my heart, healing to my soul, and wholeness to my spirit. Let Your Spirit empower me to stand firm on the wonderful truth in Your Word. Let me be endowed with the wisdom, words, and grace to provide comfort to others, who are facing difficult trials of their own. 
In Jesus's name I pray. Amen.