They must've been talking about the best solvent to use during an organic reaction. Ether is great for a lot of reasons, and is especially useful in forming the grignard reagent (organomagnesium).
Typically you've got two choices of solvent for reactions in organic chemitry: polar or nonpolar
polar is good for reactions that occur via carbocation intermediates (sn1, e1), the polar solvent stabilizes the formation of a carbocation.
However, if you use a polar solvent during sn2 or e2, then your strong nucleophile or strong base will be impaired/solvated by the solvent. Consequently a nonpolar solvent is preferred in these conditions.
Whether something dissolves will likely be a separate (gen chem) concept, such as what layer a compound enters in a sep funnel.
I actually came across a similar dilemma when solving a question regarding ether formation. The passage stated that the alkoxide anion [ (CH3)3CO- ] can be used in simple nucleophilic additions (attacking PRIMARY alkyl halids with no beta substituents). The mechanism was shown, revealing no carbocation formation, therefore we can infer that the reaction is Sn2.
I learned that for favorable conditions, we want a Polar solvent in order to stabilize the charged species (the nucleophile, and the high energy pentavalent transition state).
What it really comes down to is whether we have a PROTIC or APROTIC solvent because ALL substitution reactions and elimination reactions utilize a polar solvent. Therefore, it's kinda irrelevant.
But yes it's true that when making solutions, like dissolves like (polar and polar vs nonpolar and nonpolar)
SN1 = PROTIC SOLVENT (a solvent that can hydrogen bond)
SN2 = APROTIC Solvent (inability to hydrogen bond)
For SN2
We would want an APROTIC solvent because we don't want the nucleophile (the alkoxide ion, a very strong base) to be cluttered with protons around, and therefore obstruct the nucleophile with steric hindrance. We also don't have a carbocation, in which we would need a PROTIC solvent to stabilize it.
MORE importantly, it is the fact that Sn2 utilizes a strong nucleophile or strong base that if a protic solvent were present, it would react with the solvent, abstracting the hydrogens, just as monkeyvokes says, hinders the ability of the nucleophile.
Therefore, solvents such as Benzene, ethers, anything that can't hydrogen bond, will allow the SN2 reaction to proceed.
