Psalms 105:1-5 (KJV)

1 O give thanks unto the LORD; call upon his name: make known his deeds among the people.

2 Sing unto him, sing psalms unto him: talk ye of all his wondrous works.

3 Glory ye in his holy name: let the heart of them rejoice that seek the LORD.

4 Seek the LORD, and his strength: seek his face evermore.

5 Remember his marvellous works that he hath done; his wonders, and the judgments of his mouth;

Following these verses are listed many of the major deed of the LORD, from Abraham to possessing the land of Canaan which He promised to Abraham. Also in our reading plan in Acts 13:17-39 Paul in his preaching lists what the lord did from the time of Egypt to Jesus Christ.
God uses the sharing what GOD did in the bible and in our lives (testimonies) to encourage and to point people to Him.
We can talk and sing about His wondrous works. 
This brings glory to Him and brings joy to the believing hearer.
Telling about Jesus Christ works in our lives encourages and exhorts the listener to to seek the LORD and His strength. When we do that we also are one of listeners and through this our faith is build up in times of difficulty. 1 1 Samuel 30:6 (KJV) And David was greatly distressed; for the people spake of stoning him, because the soul of all the people was grieved, every man for his sons and for his daughters: but David encouraged himself in the LORD his God.
Let us make known, tell, sing and rejoice about what the LORD has done. It will glorify GOD and impact the hearer. 
His work sure are marvellous!