Likutei Moharan 239:1/ליקוטי מוהר"ן רל״ט:א׳

1Contention makes it is impossible to speak. For in the main speech stems from peace, as it is written, “I will now speak peace” (Psalms 122:8). It is therefore necessary for each person, prior to praying, to accept upon himself the positive commandment to “Love your neighbor as [you love] yourself” (Leviticus 19:18), so that as a result of there being love and peace, he is then able to speak in prayer.

2However, when there is no peace and there is contention, it is impossible to speak. Therefore, even if one person wants peace, but there are those who oppose him, then despite [his desire for peace], the peace is not perfect. Consequently, it is impossible to speak and pray, even though he is a man of peace, since there are those who oppose him. {“I am peace. Yet, how can I speak? They are for war” (Psalms 120:7) .}

3This is what King David, may he rest in peace, said, “I am peace.” I am a man of peace, and were it up to me, I would be at peace with everyone. Nevertheless, “How can I speak? They are for war.” That is, even though “I am peace,” it is nevertheless impossible to speak because of the war and the dispute they wage against me, as explained above.