“There is not a moment of laxness in their determination.”

“There is not a moment of laxness in their determination” means to keep on practicing diligently in one direction, towards one goal. There is no time for laxness in our practice. The body can relax a little bit, it’s alright. The mouth can relax, it’s alright. It's okay to take a break as long as the buddha-name is not interrupted in our mind. If we chant too long, we will get tired. We have to know how to adjust our body so that it is comfortable. We can chant the buddha-name, whether we stand, sit, walk, or recline. We can also chant loudly or softly, or even silently while we move our lips. In the latter, we can hear ourselves very clearly, but others cannot. Even if we chant in silence without moving our lips, it's all the same."

Commentary on the Infinite Life Sutra