Jesus is life?

Even Gaelic has its urban myths. One of them is that 'S e do bheatha is supposedly Is E do bheatha, as in He (Jesus or God) is your life. Nice try, but no.

It's true that if you dig a bit further back into history, you come across dia do bheatha in Old Irish (yes, fortunately they wrote things down), so we have an instance of CuChulainn greeting Fergus with Fuit! Día do bethu, a phopa Fergus in the Lebor na hUidre. So while this looks a bit like it might be invoking anthropomorphised omnipotent beings, there's an immediate problem. Indeed, it's unlikely to be the Christian pantheon because the Fianna didn't do Christianity.

Bearing in mind very similar Old Irish formulae, such as

• rotbia-su fáilte "to you will be welcome"
• rotbia in failti sunda againni "to you will be welcome here at us"

it is much more plausible that the origin of this phrase was rotbia de bethu "to you will be life" with ro-t·bia being:

• ro, an Old Irish preverb (a particle which may go before a verb), a form of do meaning "to(wards)"
• -t- a marker for the second person "you", so it's a little bit like having the modern dhut "to(wards) you" sitting before the verb. But, before you go down that route, it's not dhut per se, because that was duit/dait, in Old Irish
• -bia 3rd person singular future of the verb "be"; think of modern bi(dh) e.

Over time, this would change quite regularly:

1. rotbia de bethu drops the preverb ro leaving us with
2. tbia de bethu which immediately simplifies tb- to just t- which weakens and slenderises it, giving us
3. dia de bethu, which now falls prey to the ancient confusion between de & do, giving us
4. día do bheatha which is then re-analysed to
5. dé do bheatha, which further reduces to
6. sé do bheatha and is then re-analysed, again, as
7. 's e do bheatha.

By the way, this also neatly explains why the phrase, Is E do bheatha, is seemingly ungrammatical i.e. in reference to beatha, because you would expect Is í do bheatha rather than Is é.