All the nations are invited to join in this praise to God for all the wonderful things that He has done. The psalmist has plenty of reason to give his own praise. One reason is that God has heard his prayers for deliverance and his praise. He can say that because after a time of introspection, he had determined that there were no sins that he was holding onto, trying to protect, unwilling to let of. No, he wasn’t perfect, but he didn’t have any sins that would hinder God from hearing him.
How about you? Is the reason your prayers are being answered because you are harboring some sin in your heart that you won’t let go of? When we confess our sins and know we are forgiven, we have the confidence then that God hears our prayers and praises.