Why?

1 Chronicles 16:34-36
  “O give thanks to the LORD for He is good;
For His lovingkindness is everlasting.
³⁵ Then say, ‘Save us, O God of our salvation,
And gather us and deliver us from the nations,
to give thanks to Your holy name,
And glory in Your praise.’
³⁶ Blessed be the LORD, the God of Israel,
From everlasting even to everlasting.’
Then all the people said, ‘Amen.’ and praise the LORD.”

  Give thanks to the LORD!  
Why?
for He is good.
for His lovingkindness is everlasting.

  Then say to God:  ‘Save us, O God of our salvation, and gather us and deliver us from the nations.
Why?
  To give thanks to Your holy name
  and to glory in Your praise.

At the end of David’s prayer: “Blessed be the LORD, the God of Israel,
From everlasting (before creation – in the past)
even to everlasting (eternity – in the future)

Consider this  ~

And all God’s people said, “Amen!”