Adam Clarke on Psalms 149:5

Let the saints be joyful in glory - Let them be gloriously joyful: seeing themselves so honored and so successful, let them be joyful. God has put glory or honor upon them; let them give him the thanks due to his name.

Sing aloud upon their beds - While they are reclining on their couches. At their festal banquets, let them shout the praises of the Lord. In imitation of this we often have at our public entertainments the following words sung, taken from the Vulgate of Psa 115:1 : Non Nobis Domine Non Nobis; sed Nomini Tuo da Gloriam! super Misericordia Tua et Veritate Tua. "Not unto us, O Lord, not unto us, but unto thy name give glory, for thy mercy and for thy truth's sake." Let them mingle their feasting with Divine songs. This reclining on couches, while they take their food, is still practiced in Asiatic countries.