  In the present paper we develop both ideas of D. Baki\'c and B. Gulja{\v{s}}
and the categorical approach to multipliers from E.C. Lance's book and
publications of the second author, for the introduction and study of left
multipliers of Hilbert $C^*$-modules. Some properties and, in particular, the
property of maximality among all strictly essential extensions of a Hilbert
$C^*$-module for left multipliers are proved. Also relations between left
essential and left strictly essential extensions in different contexts are
obtained. Left essential and left strictly essential extensions of matrix
algebras are considered. In the final paragraph the topological approach to the
left multiplier theory of Hilbert $C^*$-modules is worked out.
