I have read a few and like his take on relationships and duty, especially in the father-son relationship. Instead of one of these, however, I have chosen 'Wedding Day'. This purposely sounds as if the poem will be celebratory but, as you will see, the first line removes that possibility.
I am afraid.
Sound has stopped in the day
And the images reel over
And over. Why all those tears,
The wild grief on his face
Outside the taxi? The sap
Of mourning rises
In our waving guests.
You sing behind the tall cake
Like a deserted bride
Who persists, demented,
And goes through the ritual.
When I went to the gents
There was a skewered heart
And a legend of love. Let me
Sleep on your breast to the airport.
More of a funereal tone overall, with the 'tears', 'grief', 'mourning'. Underneath this, though, there is a message: Love is not defined by the custom of marriage. Heaney wants to escape the superficiality of it.
Take the first line. It does not give a complete complement with a genitive to tell us what he is afraid of. It cannot be that he is afraid of marrying the wrong person because the last line reveals an intimate love for the bride; 'sleep' is when a person is most vulnerable and yet he implores the woman to allow him this privilege.
Heaney does not clarify who any of the people are in the poem, except perhaps the bride (although even this is only a simile). We could take the male with 'wild grief on his face' as the father of the bride for he might feel as though he is losing his daughter, especially if he dislikes his son-in-law. It could also be the narrator looking back in a removed position on himself as the 'images reel'. He could be remembering his own sadness as he pleases those around him, his 'guests', although they are in 'mourning' as well.
The final image is of the 'airport'. This initially implies the couple are going on their honeymoon. However, I am considering a few other ideas: the marriage means they are moving abroad, not only taking a holiday, and so he is afraid of the change that comes with the marriage; they have decided not to get married in this way and are therefore running away from the expectation of a marriage and the 'ritual' as he has visualised before it happens and is avoiding due to his fear.
Perhaps none of my theories are what Heaney intended but they all share the key idea that marriage puts a strain on love and relationships without any product which the narrator is pleased with. This is conveyed as marriage warps his perception of love when he goes to the toilet and sees a 'skewered heart'; a violent, trapped and wounded portrayal of those in love, mimicking how trapped he and his bride feel with the 'ritual'. In fact his bride feels trapped to the extent of loneliness, conveyed in the past participle 'deserted'. Maybe she feels her family have deserted her by forcing her into marriage, or maybe she does not love the man as much as he loves her.
I'm sure if I had a verbal conversation about this poem I would make up my mind about what I feel the poem is suggesting; class discussion always helps me see the flaws in my opinions.