CHRIST IS RISEN - not he "HAS" risen.
Even the Sadducees - faithful Jews - were not convinced that there is a life after death. When Jesus raised Lazarus from the dead, he was therefore pulling him back from the darkness of nothingness into the light of life. However, they decided, after seeing Jesus' awesome miracle, to kill, not only Jesus, but Lazarus too!!!
Thus Jesus' Resurrection from the dead, the most awesome of miracles, still does not force us to believe. But for those of us who DO believe, his Resurrection is a promise of what we most long for - eternal life, everlasting happiness with the Risen Lord.
And this is what we mean when we say: "Happy Easter!"