Saussure pointed to that language is mistakenly thought of as a matching of a thing to a name. To him the link is between a concept (signified) and a sound pattern (signifier). The signified is its meaning and the signifier is the “container”. The two together makes the linguistic sign.
The linguistic sign has two characteristics. One is that the link between signified and signifier is arbitrary. There is no natural link or reason that the concept should connected to its “container”. Secondly, the signifier is linear temporally and physically. It is a thing in its own right.
Furthermore, the value of a sign is summarised thus:
A language is a system in which all elements fit together, and in which the value of any one element depends on the simultaneous coexistence of all the others.
And so, “in the language itself, there are only differences“.
Reference: Course in General Linguistics, Saussure.