3 purposes for testimonies- Jesus. Others. You.

John the Baptist was not a weak Christian yet he too needed some assurance that the Lord was still there and was real! He asked, "Art thou he that should come or do we seek another?" Maybe he was wondering, why hadn't he come to help him out of his troubling circumstance. But to a discouraged saint, who maybe started to get weary in his faith, the Lord said to tell John, in Matthew 11:5, "The blind receive their sight, and the lame walk, the lepers are cleansed, and the deaf hear, the dead are raised up, and the poor have the gospel preached to them." This tells me that hearing what God has done in the lives of others helps our heart just as much sometimes as God doing it in our own.  This is why I love hearing others testimonies. The Lord knew how to comfort the great John the Baptist heart, and He did it by saying, "Go and show John the things which you do hear and see:.." 
John wanted God to show himself real to him but yet God showed him how He had been  real for others!!! Amazing how that works! How great it is during a church service or a revival meeting to hear a testimony of God giving your brother victory over bitterness, or your sister victory over an attitude or another healing over a 7 year long hurt in their heart, and God speaking peace to this ones heart or opening the eyes of one who was blinded in their sin and now they see and just on and on and on. And all you can say is, "Yes Sir,  He's the one that should come!!!!!" We need not seek another!!!"