3 “In my life.” Now what has it? It might answer you, “My death.” Whence, “My death”? Because I am absent from the Lord. For if to cling to Him is life, to depart from Him is death. But what comforts you? Hope. Now you live in hope: in hope praise, in hope sing. Your death is from the sadness of this life, you live in hope of a future life. And how will you praise your Lord? “I will sing unto my God, as long as I have my being.” What sort of praise is this, “I will sing unto my God as long as I have being”?
Behold, my brethren, what sort of being this will be; where there will be everlasting praise, there will be also everlasting being. Behold, now you have being: do you sing unto God as long as you have being? Behold, you were singing, and hast turned yourself away to some business, you sing no longer, yet you have being: you have being, yet you sing not. It may be also your desire turns you to somewhat; not only do you not sing, but thou even offendest His ears, yet you have being.
What praise will that be, when you praise as long as you have being? But what means, “as long as I have being”? Will there be any time when he will not be? Nay, rather, that “long” will be everlasting, and therefore it will be truly “long.” For whatever has end in time, however prolonged it is, is yet not “long.”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)