No mystery here - other than the mystery of Christ's sacrifice, of course.   The processional cross is, just as one might guess, a cross that is carried in procession, that is when "advancing from" (the meaning of the Latin term "processus") one place to another.

The processional cross is used, not just for the procession at the beginning of the service, but: 1) to lead the children to/from church school, with the ceremony they deserve, 2) for the reading of the Gospel and 3) at the service's end, when we recess - with the cross always in the vanguard, leading the way, as it were.

Now the clever and careful observers among you will note that we are blessed to have two processional crosses here at Trinity.

The small wooden cross, affectionately known as the "Children's Cross," is used to lead our youngest members to church school, but also for those times in the liturgical year when the stark simplicity of the wooden cross is more appropriate than the resplendent, and somewhat ornate, character of the larger, brass, Processional cross; Lent is one of those times when "less" is "more."

However, whichever processional cross is used, the question that remains is "why do we process a cross in the first place?"

Well back in the early church, when Christianity became the official state religion of the Roman Empire, Bishops and other important church dignitati came in to their own... their own cross that is.   That is to say, whenever a Bishop visited a parish, he - and it was "he" back in those not so halcyon days - was always preceded by an acolyte carrying a cross.

Over time, more and more "(self) important clergy" wanted a cross to lead the way for them as well.

Ultimately, everyone was doing it and the processional cross led the way, not just in the liturgy, but in liturgical change and renewal as well.

Since Bishops were not getting their due respect anymore, the custom developed that, when a Bishop was present, the front of the processional cross always had to face him (they were usually crucifixes back then - ie., adorned with the image of Jesus on the cross)

Fortunately this vain, glory-seeking nonsense (or vainglory-seeking if you'd rather) is no longer practiced.   Nowadays, the cross always faces the same direction as the people for whom it is preparing the way, whether or not a prelate is present.

This makes obvious sense, since, Jesus is the one we are supposed to be following anyway; moreover, especially in Lent, there is no other way for us, the people of God, to go than the way of the cross.