Psalms 98:1
O sing unto the LORD a new song; for he hath done marvellous things: his right hand, and his holy arm, hath gotten him the victory. O sing unto the LORD a new song; for he hath done marvellous things: his right hand, and his holy arm, hath gotten him the victory.
O sing unto the LORD a new song is called for because God has done marvelous things and has gotten Himself the victory. That victory is the plan of redemption accomplished through Christ. The plan was devised by the Father and the Son to ransom humanity, and it was fulfilled when Christ gave Himself for the fallen world. Christ's sacrifice as the world's Redeemer reveals the Father's love and upholds the holiness of His law.
God's right hand and His holy arm getting Him the victory describes Christ's triumph in completing His work of redemption at the cross through His death. His death came only after He had finished the work He came to do. He remained faithful to His Father through death despite relentless temptation and suffering brought against Him by Satan.
By this victory He defeated Satan and made the loss of Satan's kingdom certain, defeating Satan's attempt to retain supremacy. His victory secured humanity's ransom from eternal death and sealed the doom of the one who held the power of death. The completion of redemption brought joy and triumph in heaven. Its fruits are secured and shared by human beings, by angels, and by the unfallen worlds.