Question:
How should we witness to a non-christian that is bitter against God?

Answer:
Bring God’s love before him, and how the Lord helps the Christian who has trials. Tell of what David experienced: “I sought the Lord, and He heard me, and delivered me from all my fears” (Psalm 34:4). Tell him that God is the only source of comfort. “Blessed be God, even the Father of our Lord Jesus Christ, the Father of mercies, and the God of all comfort” (2 Corinthians 1:3).

In 2 Timothy 2:9-13 Paul tells that God uses our trials to bring the Word of God before others, and there is a future reason for trials, for if we suffer we shall reign with Christ. He is using our trials to teach us to accept everything as from His all-wise hands, and thus He is preparing us for His coming kingdom.
In addition, God will always provide a way for the Christian to bear the trial (1 Corinthians 10:13). The Lord can help us in our trials because He has suffered and felt the same. He can completely relate to everything that happens to us because He was tempted in every way that we are, but He didn’t sin (Hebrews 2:18; 4:15,16).
We might not like the trial at the time, but in the long run it will help us to grow in the Lord’s things (Hebrews 12:2-11). God has something good for us in everything that happens to us (Romans 8:28). And we can quench all the fiery darts of the wicked by the shield of FAITH (Ephesians 6:16).
Acrostic:         Forsaking

                        All

                        I

                        Trust

                        Him