Does licensing the forbidden—such as selling 'araya and wearing silk—out of need or necessity contradict the perfection of certainty in God, and is the justification for that the claim that it is a matter of certainty in God's mercy?

We do not know of any scholar who has stated what the questioner has quoted from this person, and this is sufficient to refute it. It is not permissible for anyone to speak about the religion of Allah without knowledge, for speaking about Allah without knowledge is the most forbidden of all prohibitions and the greatest of sins, as it involves lying about Allah and altering His religion. It is the root of polytheism and disbelief. This mentioned statement is pure falsehood and absolute error. The principle: "Difficulty brings ease" is one of the agreed-upon universal jurisprudential maxims. It is from Allah's mercy upon His servants and the completion of His favor, as Allah Almighty linked it with the context of gratitude in His saying: {This day I have perfected for you your religion and completed My favor upon you and have approved for you Islam as religion. But whoever is forced by severe hunger with no inclination to sin - then indeed, Allah is Forgiving and Merciful.} The Prophet, peace and blessings be upon him, also informed us of Allah's love for taking His concessions and His lightening of burdens upon His servants, saying: "Indeed, Allah Almighty loves that His concessions be availed of, just as He dislikes that His disobedience be committed." Furthermore, legitimate concessions do not contradict the perfection of certainty in Allah, because they are based on Allah's names and attributes of mercy and wisdom.