If ALL Scripture is God-breathed and profitable for teaching, doctrine and so on (2 Timothy 3:16) then I cannot understand how a sex manual can fulfill this standard for those single people who read and believe and love the Word of God. However if primarily the book draws us to a picture of Christ and His passionate love for us, and secondly is profitable for married couples then we can be mightily blessed learning about our Lord and Saviour and then rejoice for those married among us.
Ed Goode cites seven reasons for reading the Song of Solomon and they are so helpful;
1) The Bible is a book about the Father seeking out a bride for His Son. Why does everything exist? For this reason, so that we can know the Father through intimacy with the Son. Reading the Song Christocentrically (it's a word now!) fits far better into the flow of the story of the Bible.
2) Amos wrote about Heaven as a farm, Ezekiel as a temple. Why wouldn't Soloman wax lyrical about the coming King in terms he was familiar with?
3) You have to do odd things to the text to make it speak of human relationships first. Why do vineyards and gardens and trees become anatomical parts? Why can't a garden be a garden? And a vineyard a vineyard. Do we meet gardens and vineyards elsewhere in the Old Testament?
4) I think if the Song was about Soloman going to court, and being let off the punishment due his treason against the King, we'd have no problem reading it Christocentrically. (still a word!) I want to/hope to blog about this more in the coming days, how God reveals Himself as love, and yet we think of Him as law, about how our affections must drive our will and not the other way around. The Bible ends with a wedding feast, it doesn't end at the judgement. I don't think John was given his revelation in a haphazard, meaningless manner.
5) This mystery is profound and Paul says it refers to what?
6) Look at some of the imagery in the Song. What is that coming up from the wilderness like columns of smoke? (3:6) The wilderness! A column of smoke! A. Column. Of. Smoke! I mean what do we want, the groom to say he burns like a bush as he looks for his beloved?! The groom seeks, the groom is rejected, the groom wins his bride and they are united. The bride longs for the day when she and her groom are united forever. The final verse reads 'make haste my beloved, and be like a gazelle or a young stag on the mountains of spices.' What is that if not 'come Lord Jesus!'
7) I don't believe we do violence to the text reading it this way, i think we allow the text to burst forth in its glorious colour. We can still learn about human marriage from it, but again, what is marriage about? I am married so i can learn (slowly) and demonstrate (poorly) to a watching world the glories of Christ love for the church.
I really think we need this emphasis in the church today. Yes, Christians have a personal relationship with Christ, but that's not all we have. We have a relationship with our church, and Christ is coming back for His church. Your personal relationship isn't all there is. If you want a real relationship with Jesus, you'd better fling yourself into the local church. And boy, does Jesus ever love the church! Why would you not want to be involved?
You can read far more helpful and coherent thoughts here and here