Sing to the Lord a new song

Sing to the Lord a new song; sing to the Lord, all the earth.
Sing to the Lord, praise his name; proclaim his salvation day after day.
(Psalm 96:1-2)
Sing to the Lord a new song, for he has done marvelous things; his right hand and his holy arm have worked salvation for him.
The Lord has made his salvation known and revealed his righteousness to the nations.
(Psalm 98:1-2)

God leaded me to read this verses, I was just wondering, why "sing to the Lord a new song" was initially stated again and again? And it is a new song to sing. Silently I asked myself,
"Am I cannot sing to God?" or I shall say it in this way,
"I do not want to sing to God?", "Am I?"

I just think that sometimes when we go through many difficulties, and undergo certain unspeakable endurances/sufferings for quite some times. And then, when we hear of the advise from above or from people around us, and later, perhaps, there could be several reactions,
Negative Way:
1. We may harden our heart, we sing, but we are not praising and worshiping the Lord.
2. With unpleasant emotion, We don't want to sing.
Positive Way:
3. We feel like don't want to sing, but we still continue to sing, we pray for God's mercy and help.
4. We sing, we weep, we recognize Him our God.
5. We surrender, we sing, we pray, we go on follow Him till the end of the world.
......
what else?

For me, I think, honestly to say, "I need to pray for God's mercy and love." (helps)
Why sing?? It is very obvious, because of the reason, He has done the greatest thing for us - SALVATION.
HE GAVE US A NEW LIFE, HE DELIVERED US FROM THE DEATH.
Still Can't we sing to HIM?? Where have all the thankful hearts gone?
s