We already discuss this topic a lot, in much more depth than a simple rebuttal of “only a figure of speech”. You’re welcome to read any of those threads and comment there.
If you care to quote Smith’s argument for us to respond to, then please do so. Otherwise anyone could reply just as simply “the context of the saying definitely means more than only a figure of speech”.
Rather than replying to this thread he already started, Garf/Jeff tried to start two new threads asking where “all in all” discussion has taken place. I’ll quote his request here:
Would anyone like to do his research for him (he may not know how) and provide him some links?
I tried all in all in the forum search and didn’t find anything- any ideas?
I found 10 pages worth of “all in all” refs on the forum. I suspect more would be turned up if I searched for “1 Cor” (since most discussion of 1 Corinthians on this forum will naturally be concerned with 1 Cor 15:23-28.)
We don’t have a good way of getting to the advanced search features of the site. A search has to be run with the basic search thingy on the upper right first (I guess), and then click on the “Advanced search” hyperlink on the subsequent page.
Here it is for immediate reference. I think Alex has something on his to-do list about adding this as a hyperlink to the general page format. search.php
Once on that page, put “all in all” (with double quote marks around them) into the custom Google search at the top of the page. (Or “1 Cor”.)
Very briefly it may be said that this is connected to Paul’s statement earlier in 1 Cor 3:21-23, against the tendency for his (largely Greco-Roman) Corinthian audience to treat the disciples and even Christ Himself as competing philosophical factional teachers (philosophical schools at the time being tantamount to cults of personality), “So then, let no one boast in men, for all things belong to you–whether Paul or Apollos or Kephas or the world or life or death or things present or things to come: all things belong to you!–and you belong to Christ!–and Christ belongs to God!”
Moreover, as I have noted several times on the forum in the past (and others as well), the context of the verse indicates the sense in which God is all in all: all things, including the final enemies, shall become subjected to Christ after the wrath of Christ in the day of the Lord to come (thus after death and after resurrection and after the post-resurrection punishment of the unjust), at which time Christ shall subject Himself or be subjected to the Father (Who subjected all things to Him) so that God will be all in all.
The subjections of all things to Christ and of Christ to the Father are thematically and grammatically parallel. The only difference grammatically is that one is 2 Aorist Passive/Middle form (indicating here, with the {hotan} or whenever, a future accomplished result at an indeterminate time) and the other is a 2 Future Passive/Middle form (indicating either that Christ shall be subjected or shall subject Himself to the Father). If Christ subjects Himself to the Father, as the context otherwise would indicate, then all things similarly subject themselves to Him; but if Christ is subjected to the Father (although that would have to be by His own action in any case) other things are still subjected to Christ with the same subjection in which Christ subjects to the Father. (The first subjection is even 3 person singular like the second, even though its referential noun “all” is plural!–because that emphasizes the unity of the multiple persons involved.)
This is also exactly why annihilationists treat the testimony here as meaning that Christ must be annihilating the evildoers out of existence–otherwise it would be testifying to their eventual salvation from sin. And that has to be false, right? 
Furthermore, the subjection of all things to Christ (and even of Christ to the Father!) must be of a sort that doesn’t yet apply until that point in the process. But Christ was already Lord (and has been Lord/ADNY/YHWH from on high or from all eternity) in Godly authority and power and deeds; and in this scene Christ is already lord in the sense of being the direct and obvious king (or despot in the Biblical Greek, although that term isn’t used here) of all things even rebels whose rule and power and authority He has not yet abolished–for He cannot and does not hand over all things to the Father until that abolition has been accomplished. Yet that abolishment or nullification (literally down-un-acting) hasn’t been accomplished yet in His rule even in the Day of the Lord to come when He is reigning over His enemies!
So what abolishment of them remains? How are His enemies clearly under His feet and yet not-yet under His feet? For He must reign until He puts all enemies under His feet. Then He gives up His reign to the Father, Who has put all things in subjection under His feet.
The whole thing is set up as an already/not-yet comparison, where in one way Christ is reigning already and all things are in subjection to Him, but in another way Christ has not yet abolished all rebellion and all things are not yet subject to Him.
Annihilation doesn’t solve the riddle, because annihilated things stop existing and so stop being in subjection to Him, besides which they were already as subject to Him as they were going to get: so describing their annihilation as being more subjected to Him makes no sense. But in eternal conscious torment the rebels are also as subjected to Him already as they are ever going to be.
The events being described here have to involve:
1.) rebels already being subjected to Christ in several ways;
2.) rebels becoming subjected to Christ in a way beyond how they’re already (in several ways) subjected to Christ;
3.) all things, including rebels up to the final enemy, becoming subjected to Christ in the way that Christ subjects Himself to the Father–thus rebels, who are still rebels at the time of the resurrection, subjecting themselves to the Father in union with the Son;
4.) the Son ceasing to reign in some fashion after this has been finally accomplished, while still clearly reigning in other ways.
Purgatorial universalism meets these criteria. I don’t find that anything else does. To the rebels, the victorious Christ is merely a despotic king of the sort that they would prefer to be someday. Any worship they give Him is merely lip service (of the sort God elsewhere rejects!)–as all non-universalists also agree (insofar as they acknowledge rebels worshiping Christ as sinners at all.) Christ reigns over them as a king over rebellious subjects. But this comes to an end when all things subject themselves to Christ so that Christ can subject Himself and all things in Himself to the Father.
Thus God comes to reign altogether in all, not merely externally over all (which sinners have to grudgingly allow concerning the victorious incarnate Christ), but in all persons–which cannot be true about any remaining rebels.
That is exactly what “all in all” means in 1 Cor 15. 
(See also my article here on corroborating OT citational references from the end of 1 Cor 15, in regard to the victory of the coming general resurrection.)