The lines you mention are a rhymed couplet:
Ru men yin lu xu kou shou,
Gong fu wu xi fa zi xiu.
Rumen, as you’ve discovered, means to “enter the gate,” but this phrase has a long history of being used analogically for “crossing the threshold” into training, or becoming privy to important knowledge or wisdom. In the Confucian Analects, for example, Zigong, in reference to Kongzi’s teachings, remarks, “Unless one is able to enter the gate, one cannot see the beauty of the ancestral temple or the richness of the estate.” The following phrase, yinlu, means “to lead the way” or to be led the way on a path. The graph xu means “must” or “requires.” The final compound, koushou, means “oral instruction.” So, I render the line:
“Entering the gate and being led to the path, this must come from oral guidance.”
The next line begins with gongfu—“effort” that leads to accomplishment. Wuxi means “without pause.” Fa means “method,” or “to model.” The final compound, zixiu, means “self training,” or “self cultivation.” I render the line: “To ceaselessly exert oneself in the method is self-cultivation,” or “is the method of self-cultivation.” This second line is difficult to translate, as it can be interpreted differently depending upon how you parse it. For example, T. T. Liang rendered it, “If one practices constantly and studies carefully, one’s skill will take care of itself.” Yang Jwing-ming, on the other hand, translates: “practice without ceasing, the way is through self-study.” But in general the couplet refers to the necessity of being accepted by a teacher and receiving direct instruction, and the further necessity of pursuing individual training.