I am, honestly, reading authors other than Herbert McCabe this Lent. But this, from an Ash Wednesday sermon, struck me as succinctly getting right the purpose and dangers of Lenten almsgiving. Having already spoken about fasting, McCabe says:
The other side of fasting is almsgiving, helping those in need. But here, too, remember that we are engaged in a drama, a symbolic act. We do not give alms in Lent because we are under the illusion that almsgiving will solve the problem of world poverty; and by the same token we do not think it foolish to give alms just because we know it will not solve that problem. The point is again to dramatize for ourselves the reality of poverty and oppression and need, and of our responsibility in the face of it. Almsgiving is not a substitute for political action. Art is not a substitute for reality.
(God, Christ, and Us. p. 77)