Why does all of the savings in the economy create an equal amount of investment spending according to neoclassical theory and Keynesian model?

In neoclassical theory, savings provide the funds necessary for investment, as they are channeled through financial markets to businesses seeking to invest in capital. This creates a direct link where all savings translate into investment spending, assuming full employment and efficient capital allocation. Conversely, the Keynesian model emphasizes that while savings can lead to investment, they may not always match due to factors like demand fluctuations; thus, savings can sometimes lead to a decrease in overall economic activity if they are not spent. Ultimately, both theories recognize a relationship between savings and investment, but they differ in the mechanisms and conditions under which this relationship holds true.