Something which is ‘personal,’ in the sense of the word which is here relevant, is unique to an individual, or has a unique relation to a particular individual. We speak of a wealthy individual as having a ‘personal’ fortune, or a celebrity making a ‘personal’ appearance. In those examples, the fortune is peculiar to the individual, and nobody else could have made a ‘personal’ appearance for the celebrity.
By contrast, ‘private,’ in the meaning here pertinent, refers to something which is confidential, secret, or undisclosed.
Our faith is always personal, but never private. God calls us to live in a community.
Each of us has a unique relationship to God. Each of us lives out our faith in a unique way. God calls each of us to unique tasks.
But this uniqueness occurs in the context of fellowship. We often pray alone, but sometimes corporately. We often study Scripture alone, but sometimes together. We worship both individually and as a group.
This is reflected in the language of Scripture.
In older English translations, we encounter the word ‘thou’ and in fact, this word has become, in some circles, the hallmark of classic or traditional religious discourse, for good or for ill.
But in those historic translations, the word ‘thou’ is used alongside the word ‘you’ – in, e.g., the King James Version, also called the Authorized Version.
The difference is significant. ‘You’ is plural; ‘thou’ is singular.
Note the various, between the plural and singular second person in, e.g., the early chapters of Deuteronomy (‘thou’ and ‘you’). Is God, through Moses, talking to each individual, or to the whole community?