Well, I am again in the religious, but I do think it is an important part of Jane Austen's meaning.
I do believe each portrait of her heroes show a part of the inspiration of Christian marriage, here particularly as told by St Paul to Ephesians (read at most Christian marriages) :
"22 Wives, submit to your own husbands, as to the Lord. 23 For the husband is the head of the wife even as Christ is the head of the church, his body, and is himself its Savior. 24 Now as the church submits to Christ, so also wives should submit in everything to their husbands.
25 Husbands, love your wives, as Christ loved the church and gave himself up for her, 26 that he might sanctify her, having cleansed her by the washing of water with the word, 27 so that he might present the church to himself in splendor, without spot or wrinkle or any such thing, that she might be holy and without blemish."
Darcy's action is mainly relevant to 25-27.
Elizabeth's character was soiled by Lydia's elopement. To restore her he "gave himself up for her" : "He had followed them purposely to town, he had taken on himself all the trouble and mortification attendant on such a research; in which supplication had been necessary to a woman whom he must abominate and despise, and where he was reduced to meet, frequently meet, reason with, persuade, and finally bribe, the man whom he always most wished to avoid, and whose very name it was punishment to him to pronounce."
To me there is a clear parallel with Christ's Passion, it was, as you say, "His choice", there was no obligation, and it redeemed the sinners (here Elizabeth has not sinned but is stained by her sister's behaviour), and St Paul teaches it is one of the husband's "functions".
Sorry if these religious considerations hurt any of you, but I do believe they are very clearly underlined in Pride and Prejudice.
Sorry too, for having had so little time to write it, I hope it is understandable.