Grace=Forgiveness - an awesome yet entirely strange concept

The whole idea of God's Grace is a strange one. Grace states that we are all sinful and yet God will forgive us if we ask - even though we do not deserve it. It follows then that if God forgives us then we have very little right not to forgive others - passing the judgement and the weight to God; the ultimate judge.
This is the sort of thing I have read about in textbooks for years - I even teach about it(!!) sometimes and yet I have never really, truely understood it. It took some time and many an analogy from my Pastor to get it but when I did it was a PHYSICAL feeling of recognition. No so much a EUREKA! moment but a realisation of the weight that I am carrying on my back through my unforgiveness. I feel like the person I have not forgiven is still there clinging on to my back, through everything that I do I am carrying the hatred and it's suffocating me.
The idea that I can get rid of that makes me feel lighter and happier than I thought possible - but it is only a fleeting feeling - something I can't grab. As Michael Jackson once wrote in his song 'Gone too Soon' it's like 'a castle built upon a sandy beach...here one day, gone one night'.
So i guess that this is a glimpse of the feeling that all these people at Church are harping on about. I guess this is the feeling of the Holy Spirit at work in my heart.
So here's the clincher...I figure that in order to live in this light - in God's light then I must have to do something positive, CHOOSE to forgive and actively pray for His help everyday because I'm not sure that all of e wants to forgive. I've got to invite God into my life...and actually let Him take the wheel................Cue feelings of fear and joy. A strange feeling