You said the dates are totally irrelevant [implying that looking into the matter is a useless exercise]. I showed you that you are being inconsistent since you in fact celebrate Christ’s birth every 25th of December – the same date every year. If the date makes no difference to you, why celebrate Christmas every year on the same date?
The Church through the calculations described in Patrick’s post tells us when Good Friday will be and shows that the date of Good Friday each year is different. Neither the Church nor we know the actual date Christ was crucified. The actual date of his crucifxion is not relevant to our faith or salvation (even though it would be interesting to know).
I hope you know that these calculations are based on some assumed date of the crucifixion. You cannot make the calculations unless you have a starting or reference point. By celebrating the day arrived at from these calculations, you are acknowledging the relevance of the date on which those calculations are based upon.
As for the actual date of the crucifixion being totally irrelevant, not so. The exact year may not be important but the month and day is. Following Christ’s example, we are to celebrate the Lord’s Supper “when the hour [is] come” (Luke 22:14) – that is, at the set time and day when that time period comes around each year.