Singing comfortably is different than a ”weak” or ”soft” voice

A student was instructed by his vocal trainer to, ”Be more effortless when singing a song.” Consequently, his voice got quieter when he was supposed to sing louder and more powerful. Relaxation and being comfortable play a major role in the delivery of the sound produced.
“Effortless” was referring to, that you should focus on only relaxing unnecessary muscles for phonation, not the whole laryngeal muscle. “Singing louder and more powerful” is different than a “weak voice” or “small voice.”
The average person has approximately 630 muscles (mainly voluntary muscles) in the body. Most of the muscles can detect the hardness and movements when produced. The muscles of the throat cannot detect the hardness or movements.
For instance,when you say “pa” or “i”, do you know to what degree of strength you are using in your muscle, exactly?
–  or when you vocalize tone “C” or “A”, do you know to what degree of strength you are using with those muscles?
No, because, it is impossible to determine.
The thought is planted and movements are followed through by the brain, but simultaneous awareness of the amount of strength being issued to each specific muscle group at the time of the movement is something that has to be learned through practicing, focusing and vocal training.
Therefore, if you act too loose or comfortable while singing … for example,  completely relaxed, all the muscles relating to phonation will get flaccid, and it is harder to vocalize and/or control the movements.
Let’s compare the vocal movement to a body movement such as jumping. If you want to jump high, you have to bend the knee and use the muscles in the thigh and leg region. You cannot jump without stretching out your legs.
So, if your knee is hardened or the muscles are tense, you cannot jump. That is why, you have to soften the movement around the knee to jump high.This does not mean that the muscle is relaxed in the thigh and leg region.
Which muscle should be relaxed and focused for phonation?
First, relax the pharyngeal constrictors, (especially the superior, middle and annular part) then the stylopharyngeus muscle, the stylohyoid muscle, the digastric and the omohyoid muscle. Simultaneouly, and constantly move the cricothyroid muscle, the posterior cricoarytenoid muscle and the lateral cricoarytenoid muscles. The former relates to the environment of the movement and the latter relates to the pure natural movements such as expanding the vocal chords (for high pitch) or closing vocal chords (glottic closure).
It becomes possible to make your voice more loud and rich if you can control this, and utilize this technique correctly.
I would like you to practice and learn to relax your throat properly, which will in turn make your voice better.