Sometimes, when [you feel that you are] unable to pray, do not believe that you are definitely unable to pray that day. Strengthen yourself all the more 1 and the awe [of God] will come upon you ever more. 2

This is comparable to a king who sets out to wage war and disguises himself. Those who are wise recognize him by his mannerisms. Those who are less wise recognize the king by noting the place with extraordinary guarding: surely that is the place of the king. 3

Thus it is when you are unable to pray with kavanah. You must know that there is additional guarding all around the King. The King is there, but you are unable to approach Him because of the special protection surrounding Him. Thus fortify yourself with awe, great strength and additional kavanah, so that you will be able to come close and pray before God. You will then be able to pray with exceeding kavanah.