As with any quote, historical context is important. Pope John XXIII lived in an era when single‐parent families, and cohabiting couples, were rare. And same-sex unions were inconceivable. Back in the late 1950s and early 60s, "family" meant a married father and a mother, and children. There was still a basic moral consensus, which could be presumed in using phrases such as "form a family." 
 
Today, this is gone, and we must be much more specific. Thus, in reading Pope John XXIII, we must adjust to the context in which he spoke, and cannot reasonably demand the precision that is necessary today. Neither would it be reasonable for our opponents on the marriage question to read into these remarks an approval for the current situation.

Such lines ought to cause concern. For, interpreted in a rather literalistic way, they seem to declare equivalence between the sacrament of the Holy Eucharist and of our communion with one another. 
 
It is true, the concepts are related, but they are not equivalent or substitutable. One in fact causes the other. That is to say, our communion with Christ in Holy Communion effects our communion with one another. And I suspect that is what these hymns are trying to get at. But they do so in a clumsy sort of way, as if the two were simply and merely the same. They are not. 
 
For Christ is not simply reducible or equivalent to the sum total of his members, but he, as God, is greater than and is the cause of the communion we enjoy with one another. 
 
That said, we must accept the limits of what art and poetry do. Hymns are a form of poetry, and cannot always have the doctrinal precision that we might expect of a theological treatise. Context is important, and hymn use a poetic genre. 
 
Nevertheless, some of the older Eucharistic hymns were able to speak politically, and yet not sacrifice doctrinal precision. Perhaps we could hope for more than we often find in many modern compositions.