This gate of the Lord, into which the righteous shall enter; rather, this is the gate of the Lord: the righteous [and they alone] shall enter by it. "This verse seems to stand apart—a solo, chanted by a voice out of the temple gate" (Kay).
Though sinners doubtless sometimes entered (2 Kings 11:13; 2 Chronicles 26:16-20; John 2:14), none but the righteous had any right to enter.