What are the wonders of the Lord? They are those that we can contemplate day by day, they are feats of the Lord so that we see His perfect works manifested in our lives.
Seeing His wonders, we rejoice in Almighty God, why do we rejoice in the Lord? Because we see how beautiful it is to contemplate His mighty wonders.
When we see the heavens and the earth, we see these works and wonders created with His powerful hand, and this dresses us with joy to see His wonderful and powerful hand working on our behalf.
Psalm 71 is a thanksgiving from David to God, so we see David saying to God these words of thanks and honor to the Lord:
O God, thou hast taught me from my youth: and hitherto have I declared thy wondrous works.
Psalm 71:17 (KJV)
Here we can see what the psalmist says to the Lord in this Psalm 71. David saw the wonders of God in his life, David could see the tremendous work that God did in each of the places where David was.
So we see how in this verse 17 David says that God taught him from his youth and manifested his wonders. And this is how this man mentions it, because many of the psalms that this man has written are of thanks and praises to God for His wonderful deeds.
It is always good to thank God for His good works, for His powerful wonders, wonders that we can contemplate every day, that we see with our eyes to God working with His mighty hands, our God is great and powerful for that, oh God! We always exalt You.