And when I am ill, it is He Who cures me.
Here he attributed sickness to himself, even though it is Allah Who decrees it, out of respect towards Allah.
By the same token, Allah commands us to say in the prayer,
اهْدِنَا الصِّرَاطَ الْمُسْتَقِيمَ
(Guide us to the straight way) (1;6) to the end of the Surah.
Grace and guidance are attributed to Allah, may He be exalted, but the subject of the verb with reference to anger is omitted, and going astray is attributed to the people.
This is like when the Jinn said;
وَأَنَّا لَا نَدْرِى أَشَرٌّ أُرِيدَ بِمَن فِى الاٌّرْضِ أَمْ أَرَادَ بِهِمْ رَبُّهُمْ رَشَداً
And we know not whether evil is intended for those on earth, or whether their Lord intends for them a right path. (72;10)
Similarly, Ibrahim said;
وَإِذَا مَرِضْتُ فَهُوَ يَشْفِينِ
(And when I am ill, it is He Who cures me).
meaning, `when I fall sick, no one is able to heal me but Him, Who heals me with the means that may lead to recovery'.
وَالَّذِي يُمِيتُنِي ثُمَّ يُحْيِينِ