Intrusive thoughts during prayer are not a sign that your prayer is worthless. They are a sign that your prayer is working.
Chapter twenty-eight of the Tanya addresses one of the most common experiences in spiritual life: you sit down to pray with concentration, and within minutes your mind is flooded with distractions—desires, anxieties, random images, fantasies. The natural conclusion is devastating: clearly, my prayer is defective. If I were truly praying, these thoughts would not arise.
Rabbi Schneur Zalman demolishes this conclusion. The reason intrusive thoughts intensify during prayer is that two souls are at war. When the divine soul gathers its strength for concentrated devotion, the animal soul responds by mustering its own forces. It is like two wrestlers: when one pushes harder, the other pushes back. The surge of distraction during prayer is evidence of the animal soul's counterattack—which only happens because the divine soul was genuinely threatening its position.
If the prayer were meaningless, the animal soul would not bother disrupting it.
The Tanya offers a parable. Imagine you are praying with deep devotion, and a wicked person walks up and starts talking to you, trying to break your concentration. What would you do? You would not engage with him. You would not argue. You would not even acknowledge his presence. You would simply continue praying, pretending he is not there.
The intrusive thought is that wicked person. It comes from the animal soul—a separate entity with its own agenda. Engaging with it—either by following the thought or by getting upset about it—gives it power. Ignoring it and returning to prayer is the only correct response.
The Tanya says you should not even try to "elevate" the thought, as some Kabbalistic practices suggest. That technique is for tzaddik (a righteous person)im (the righteous), whose intrusive thoughts come from external sources and can be redirected. For the benoni, whose distracting thoughts come from his own animal soul, trying to elevate them is like trying to lift yourself by your own hair while your feet are chained to the ground. Just ignore the thought, return to prayer, and keep going.