Depending upon where we live, & the local sheep population, shepherd imagery isn't necessarily helpful except when the principle comes close up & personal. How to make that happen? How to translate Jesus' Middle Eastern imagery, still alive & well in parts of the world though it may be, into our own local culture where shepherding has moved on. Here in Oz, shepherding will most likely be done on horseback, in four wheel drives, on motor bikes, or in helicopters. Only when the shepherd gets off or out & becomes personal to specific sheep does Jesus' imagery bite. A useful reminder that shepherding of the Jesus kind is always close up, personal, & hands on!
The / a good shepherd doesn't abandon sheep, singular or plural, because the going's become too hard. Pastor -ing is built on Jesus' promise & premise. Preaching must be pastoring, too. The relationship between Father, Son, & Spirit is meant to flow onto & into us & all our relationships with each other. Not least in our roles as sheep & shepherds.
When it comes to the 'other sheep that don't belong to this fold' I'm used to hearing inter-church relationships, ecumenism expounded. Whatever Jesus means, it can't be that. Not primariily. At face value, he's talking about those who are not Jewish & where they fit into God's scheme of things. As I'm one of them, I'm glad there's a place for me in one eventual flock, which will, of course, include those of other churches too.
I appreciate the way Jesus explains his job description at the end of this passage. There's no mention of any God-demanded sacrifice except the self-sacrifice that's the expression of total love. Total agape. Complete freedom to give & / or take up, take back life. The only 'charge' Jesus has received is to give & keep on giving. There is nothing sinister in this, compared with the way many conservatives still want to understand atonement in terms of the appeasement of an all demanding (even child-abusive?) Father figure. Let's neither preach such a figure, nor become one! That's not a figure recognizable in Jesus' teaching or actions.
A big hurdle we have to jump when we preach on this passage is the over-supply of 'cowboys' in many societies & an under - supply of shepherds!