As-salaamu 3laikum, I don't understand Surat 6 ayat 148 and 149 because in both the will of Allah is mentioned but it doesn't seem to have the same meaning each time. Can you explain. Jazaak Allahu khair.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Allaah says (what means): {Those who associated with Allaah will say, “If Allaah had willed, we would not have associated [anything] and neither would our fathers, nor would we have prohibited anything." Likewise did those before deny until they tasted Our punishment. Say, "Do you have any knowledge that you can produce for us? You follow not except assumption, and you are not but falsifying.”} [Quran 6:148]

Allaah also says (what means): {Say, “With Allaah is the far-reaching argument. If He had willed, He would have guided you all.”} [Quran 6:149]

There is no contradiction between the two verses. In the first verse, Allaah Almighty stated that the polytheists said a word of truth while they intended something false by it; they intended to say that Allaah is pleased with their Shirk and with what they declared to be forbidden to themselves, so Allaah pronounces the falsity of their claim by saying {Likewise did those before deny ...}

Al-Baghawi said: “The rejection is not of their saying {If Allaah had willed, we would not have associated [anything]} as this is a true statement, but it is of their intention, 'Allaah ordered us to do this and He is pleased with what we are doing.'” [End of quote]

Ibn Al-Jawzi said in Zaad Al-Maseer: “Allaah’s saying {Those who associated with Allaah will say...} i.e. when the proof is established against them and they realized that the polytheism that they followed was false and that them making forbidden to themselves what Allaah had not made forbidden to them was false, they said {If Allaah had willed, we would not have associated [anything]} and they cited this argument as evidence for them continuing to follow a false path. It is as if they are saying: If Allaah was not content with what we follow, He would have prevented us from doing so; but they said this out of mockery and in order to defend their argument with it, so it would be said to them: Why then do you say about your opponents that they are misguided while they are also under the Will of Allaah. Thus they have no excuse because they use the Will of Allaah as an excuse and they ignore His commands. The Will of Allaah encompasses all beings (i.e. the good and the evil) while His commands do not encompass His Will; so a person has to follow the order and one should not give excuses under the pretext of the Will of Allaah after knowing the command.” [End of quote]

Ibn 'Aashoor said in At-Tahreer wat-Tanweer: “The Will that is intended in His saying: {If He had willed, He would have guided you all} is not the same Will that is meant in their statement {If Allaah had willed, we would not have associated [anything]}; otherwise Allaah would be confirming in the second verse what He had, in the first verse, affirmed as being a falsity, and so the argumentation would be contradictory. This is because guidance is equal to not committing Shirk and to not prohibiting for themselves what Allaah did not prohibit; so it is not correct to make both a consequence of the conditional ‘if’. Indeed, the Will that is intended in Allaah's response to them is the hidden and concealed Will, which is the Will of Predestination and Decree [that Allaah has predestined and decreed] and the Will that is denied is the fact that they used what actually happened (i.e. their evil deeds) as evidence that Allaah is pleased with what they do. 

Allaah Knows best.