It’s only necessary to take refuge once. What’s more important is to cultivate understanding that refuge means abandoning reliance on conventional reality and placing full trust in the Dhamma particularly as the view of what is the goal of life, not material acquisition but self awakening. “A sense of the Dhamma” means knowing enough of the suttas to differentiate between the conventional path and the noble path.
The Buddha speaking to a layperson on the purpose of recollecting the Buddha, Dhamma & Sangha :
“And when the mind is headed straight, the disciple of the noble ones gains a sense of the goal, gains a sense of the Dhamma, gains joy connected with the Dhamma. In one who is joyful, rapture arises. In one who is rapturous, the body grows calm. One whose body is calmed experiences ease. In one at ease, the mind becomes concentrated.”—AN 11.13
Instructions on how to practise recollection are in the present sutta.