In this article, the author demonstrates that there is a huge contradiction between the statements made in the famous literature about general relativity regarding the vanishing covariant divergence of the energy-momentum tensor of matter representing a conservation law. It is reasoned which of these contradictory standpoints are correct and which are not. The author points out why pseudotensors cannot represent the energy density of the gravitational field. Contrary to the statements in the famous literature about general relativity, the energy density of the gravitational field is shown to be described by a tensor. Moreover, the author demonstrates that in general relativity there necessarily exists the conservation of total energy, momentum, and stress regarding the completed version of Einstein's field equations which is that one with the cosmological constant, whereby the latter one takes on a completely new meaning that solves the cosmological constant problem. This new interpretation of the cosmological constant also explains the dark energy and the dark matter phenomenon. The modified Poisson equation, that is obtained from Einstein's field equations with the cosmological constant in the limit of weak gravitational fields, approximately meets the requirement of conservation of total energy in Newton's theory of gravity, whereby flat rotation curves of spiral galaxies are obtained.