The main problem with your code is that you're employing an equation environment to typeset several lines of displayed math material. I suggest you use a gather* environment rather than an equation environment.
The exposition of the consumer's utility function and of the constrained maximization problem also leave a lot to be desired. For instance, the condition K_{1977}=\overline{K}_{1977} is a starting or initial condition and need not -- in fact, should not -- be repeated for t=0,1,\dots. And, the = symbol in the middle of \sum_{t=1977}^{\infty} = \beta^{t-1977} cannot possibly be correct.
The following modified exposition may be more easily accessible by readers:

\documentclass{beamer}
\usepackage{amsmath,amssymb}
\begin{document}
\begin{frame}
\frametitle{NGM with an infinitely-lived consumer}
To solve the NGM model, consider an infinitely lived consumer
with an additively separable period utility function given by:
\[
\gamma \log C_{t}+(1-\gamma ) \log(N_{t} \bar{h}-L_{t})\,.
\]
Utility maximization is performed jointly over $C_t$, $L_t$, and $K_{t+1}$, $t=0,1,\dots$:
\begin{gather*}
\max_{\lbrace C_{t},L_{t},K_{t+1}\rbrace_{t=1977}^{\infty}}\quad
\sum_{t=1977}^{\infty} \beta^{t-1977}
\bigl[ \gamma \log C_{t}+(1-\gamma ) \log(N_{t} \bar{h}-L_{t})\bigr] \\
\intertext{such that $K_{1977}=\overline{K}_{1977}$ and, for all $t=0,1,...$}
C_{t}+L_{t+1}-K_{t} = w_{t} L_{t} + (r_{t}-\delta)K_{t} \,.
\end{gather*}
\end{frame}
\end{document}
\logand\maxinstead oflogandmax. – leandriis Sep 09 '19 at 13:14