陰陽接而變化起
The Feminine and Masculine joins, initiating changes*
是故誌意隨天地,緩急仿陰陽**
It is keeping intentionally in mind that intention shall follow Heaven and Earth, in priority imitating the Feminine and the Masculine
所以必因射助陽選士者,所以扶助微弱而抑其強,和調陰陽,戒不虞也***
Then certainly because the best and brightest shoot to reinforce the Masculine, then helping the feeble while containing its strength, harmonising the Feminine and the Masculine, thus preventing the unexpected.
Any exercice, even if done perfectly, an anyway impossible feat, will still bear some armful effects on one's body, spirit...