Tonglen is a very ancient Buddhist practice, which is a subset of Lovingkindness practices. The heart of the practice – which one reaches after a number of preliminary spiritual exercises – is the taking away – in imagination – of the pain and evil of someone, and replacing it with peace and warmth and compassion. Essentially, we imagine someone in front of us, and, as we breathe in, we imagine that we are literally sucking out of that person all the pain and evil, in the form of a black cloud of toxins. And, on the out breath, we breathe into the person all our love and our peace. We repeat this process of at least ten minutes.
For the Christian, it is acceptable to do this is company with Jesus; to imagine that we are able to turn over the toxins to him. Also, we can remember that in doing this, we are in fact practising the famous Christian prayer “Lamb of God, who takes away the sins of the world…” The difference from the traditional prayer is that we are actually doing ourselves what we have heretofore acknowleged Jesus alone did. This is simply part of the great shift in Christian spirituality from letting Jesus do all the salvific work, to recognizing that Jesus invites us to follow him – i.e., to do as he does – not adore him.