"...in establishing a church."

That works for Unitarians or whoever -- who reach out theologically for the ultimate vacancy of biblical thought, not on the scale of early Christianity. But for Catholics (and most other Christians) who assent to the early church councils, the unity of the faithful was established at Pentecost, after Our Lord's Ascension, and was later fleshed out in the councils and in the planting of churches all over the known world. That ecclesial scale might not meet your fancy, Frances; but for most believing Christians, Christianity without the early Church councils gives the Trinity a shrunken head with no face; and compels the Risen Jesus and Holy Spirit to surrender to shadows on some half-opened Sinai, mountain. The Incarnation, however, enables Christ to feel compassion for all of us entangled in his redemptive history, which started at Bethlehem, continued at Calvary and the empty tomb, and is ongoing in each one of us caught up in his living church.