Reflections on Psalm 9: 1-2 from Charles H. Spurgeon:

I will praise thee, O Jehovah, with my whole heart;  I will shew forth thy marvellous works.  I will be glad and rejoice in thee:  I will sing praise to thy name, O thou most High.  

"With a holy resolution the songster begins his hymn:  I will praise thee, O Jehovah.  It sometimes needs all our determination to face the foe and bless the Lord in the teeth of His enemies;  vowing that whoever else may be silent we will bless His name.  Here, however, the overthrow of the foe is viewed as complete, and the song flows with sacred fulness of delight.  It is our duty to praise the Lord; let us perform it as a privilege.  Observe that David's praise is all given to the Lord.  Praise is to be offered to God alone.  We may be grateful to the intermediate agent, but our thanks must have long wings and mount aloft to heaven.  

With my whole heart.  Half heart is no heart.  I will shew forth.  There is true praise in the thankful telling forth to others of our heavenly Father's dealings with us. This is one of the themes upon which the godly should speak often to one another, and it will not be casting pearls before swine if we make even the ungodly hear of the lovingkindness of the Lord to us.  

All thy marvellous works.  Gratitude for one mercy refreshes the memory as to thousands of others.  One silver link in the chain draws up a long series of tender remembrances.  Here is eternal work for us, for there can be no end to the showing forth of all His deeds of love.  If we consider our own sinfulness and nothingness, we must feel that every work of preservation , forgiveness, conversion, deliverance, and sanctification which the Lord has wrought for us or in us is a marvellous work.  Even in heaven, divine lovingkindness will doubtless be as much a theme of surprise as of rapture!

Gladness and joy are the appropriate spirit in which to praise the goodness of the Lord.  Birds extol the Creator in notes of overflowing joy, the cattle low forth His praise with tumult of happiness, and the fish leap up in His worship with excess of delight.  He whose name is Love is best pleased with the holy mirth, and sanctified by the gladness of His people. "