Psalm 47 is a call for us to rejoice and praise God, the King of the earth. All the nations belong to Him. All rulers serve under Him. And He has established beloved Israel as His people and put all the other nations under them.
There are many reasons to praise God. His greatness (i.e. His power, His glory). His goodness (His mercy, His love). His wisdom. His strength. His compassion. His presence.
The reasons cited in Psalm 47 are particularly nationalistic. The Psalmist praises God because of what He has done exclusively for Israel in contrast to other nations. Such sentiment might give us pause as non-Israelites. Yet, when we join in the recognition of God as the God above all others - and our God! - we stand in relationship to Him through Jesus and share in the blessings of Israel. He extends His love to us in Christ. We also are His people!