"according to the law, men appoint as high priests men who are spiritually weak" or "for according to the law, men who are weak against sin are appointed as high priests"
"God appointed a Son by his oath, which he made after he gave the law, a Son" or "after he had given the law, God swore an oath and appointed his Son". These are important titles that describe the relationship between God and Jesus. It is best to translate “Father” and “Son” with the same words that your language uses to refer to a human father and a human son.