Of all the words spoken by Christ during his Passion, this one probably makes me the most uncomfortable. It's a challenge. It's a radical call to imitate my Lord in a way that on a lot of days I wish I didn't have to. I might even venture to say that it's even worse than the words we pray in the Our Father. There at least we pray forgive us as we forgive.
St. Thomas Aquinas explains this first word this way: "To show the abundance of the love which led him to suffer, Christ on the cross sought pardon for his persecutors. He wished to suffer at the hands of both Jews and gentiles so that the fruit of his petition might reach them both." Looked at this way, then Christ's first word is a plea to His Father for forgiveness for me, for you. That is a consolation.
Let us pray to Christ for the grace and the courage to be able to pray this first word of His as our own, so that we, too, are able to love everyone with that same love with which He loves us.