In these days after the Solemnity of the Ascension, it’s proper to reflect on the Church that our Lord left behind.
In the 1985 interview book “The Ratzinger Report“, Joseph Cardinal Ratzinger (now Pope Benedict XVI) said this to interviewer Vittorio Messori:

…the Church is not ours but his. Hence the ‘reform’, the ‘renewals’… cannot exhaust themselves in a zealous activity on our part to erect new, sophisticated structures…. Saints, in fact, reformed the Church in depth, not by working up plans for new structures, but by reforming themselves. What the Church needs in order to respond to the needs of man in every age is holiness, not management.

The Cardinal was speaking about ecclesiologies — theories of what the Church is — that had lost their balance in the 1960s and 1970s. Some Catholics, he said, had in practice adopted a concept of the Church that was like the American “free church” concept. This refers to the pattern we see as far back in America as the Pilgrims: a fellowship of believers who spurned the idea of an institutional Catholic Church founded by the will of Christ, and also spurned the state-churches that arose from the Protestant Reformation, which those Pilgrims also considered oppressive. They founded their own communities to follow their spiritual lives according to their convictions.
To think of the Church as a creation of ours makes it a human construct, subject to democratic processes and group dynamics, and dependent on our human skills of management.
This is different from how we Catholics believe. We think of the Church as the communio sanctorum, a phrase with multiple meanings.
The Church is the fellowship of the saints, in which “saints” refers to all the baptized, the people made holy (“saints”) by the grace of Christ given in baptism. This fellowship extends not only throughout the world but also through time, and includes those who have died in fellowship with Christ, and who are still one community with us even as they await their glorification which will be full at the end of the world.
And the Church even includes the Holy One himself, Christ the Lord risen and glorious who has ascended to the Father and is present body and soul before Him. The Church is the Body of Christ, present in Heaven through Him, and present in the world and in history through His people.
Because Christ is the Head of the Church, He makes the Church into the communio sanctorum in its other meaning: the sharing of holy things. It is the sharing of the sacraments — Baptism, Confirmation, the Eucharist, Confession, Ordination, Marriage, Anointing — the holy things through which Christ uses material goods, words, and gestures to confer grace and spiritual life on us. To be fully in the Church is to share the sacraments, the greatest of which is the Eucharist which contains the living Jesus Christ himself, given to us hidden under the forms of bread and wine.