In auditory neuroscience, electrophysiological synchronization to low-level acoustic and high-level linguistic features is well established—but its functional purpose for verbal information transmission is unclear. Based on prior evidence for a dependence of auditory task performance on delta-band oscillatory phase, we hypothesized that the synchronization of electrophysiological responses at delta-band frequency to the speech stimulus serves to implicitly align neural excitability with syntactic information. The experimental paradigm of our auditory EEG study uniformly distributed morphosyntactic violations across syntactic phrases of natural sentences, such that violations would occur at points differing in linguistic information content. In support of our hypothesis, we found behavioral responses to morphosyntactic violations to increase with decreasing syntactic information content—in significant correlation with delta-band phase, which had synchronized to our speech stimuli. Our findings indicate that rhythmic electrophysiological synchronization to the speech stream is a functional mechanism that may align neural excitability with linguistic information content, optimizing language comprehension.