וְקוֹיֵ֤ יְהוָה֙ יַחֲלִ֣יפוּ כֹ֔חַ יַעֲל֥וּ אֵ֖בֶר כַּנְּשָׁרִ֑ים יָר֙וּצוּ֙ וְלֹ֣א יִיגָ֔עוּ יֵלְכ֖וּ וְלֹ֥א יִיעָֽפוּ׃ (פ)
Ceux qui mettent leur espoir en Dieu acquièrent de nouvelles forces, ils prennent le rapide essor des aigles; ils courent et ne sont pas fatigués, ils vont et ne se lassent point.
Akeidat Yitzchak
The meaning of our opening aggadah is as follows. If you refrain from contact with your wife during the seven days of the menstrual cycle, tum-ah, you will merit the blessing of the eighth day, i.e. circumcision, which symbolises ascendancy over the spirit of impurity, attainment of purity. Since "seven days" represent the "creation cycle," the number seven always reminds man both of his duties and of his limitations on this planet.
Duties of the Heart
(6) The alchemist is not immune from sickness and disease which hinders his joy in being wealthy, and prevents him from benefiting from what he has and enjoying what he has acquired. But one who trusts in G-d, is immune from sickness and disease except as an atonement or to increase his reward, as written "Now youths shall become tired and weary, and young men shall stumble" (Yeshaya 40:30), "those who hope in G-d will renew strength" (Yeshaya 40:31), and "For the arms of the wicked shall be broken, but the L-ord supports the righteous" (Tehilim 37:17).