When this poem was written the debate was about the host being or not the true 'Body of Christ', hence the lyric 'verum corpus'. There is probably some subtle connection that resonated with 'taste' in the act of eating the host in communion. So in this case I think the wish in the last line is a positive one, in that the prayer is addressing the host, Christ's body, and saying may my eating your body in communion be a foretaste of the happiness and glory I will enjoy in life eternal. Not may Christ's death be a foretaste of my own death. that doesn't make much sense theologically.