Believing without deeds is not sufficient because faith is what is settled in the heart and is proved by action which is a righteous deed in which there is good for people and all of humanity. If people hope for our good and are safe from our evil, then we will be among those who do righteous deeds.
( وَمَنْ أَصْدَقُ مِنَ اللَّهِ قِيلً … ) (…and who is more truthful than Allah in statement): Truthfulness is the conformity of words to reality. Absolutely, there is no one more truthful than Allah (swt), and His promises are definitely true.
The Paradise is unseen and the Prophet (saws) said in a Holy Hadith:
“There will be bounties which no eye has seen, no ear has heard and no human heart has ever perceived.”
When Allah (swt) describes the Paradise, He begins with the word (The example), as in this verse:
مَّثَلُ الْجَنَّةِ الَّتِي وُعِدَ الْمُتَّقُونَ ۖ تَجْرِي مِن تَحْتِهَا الْأَنْهَارُ ۖ أُكُلُهَا دَائِمٌ وَظِلُّهَا ۚ تِلْكَ عُقْبَى الَّذِينَ اتَّقَوا ۖ وَّعُقْبَى الْكَافِرِينَ النَّارُ
(The example of Paradise, which the righteous have been promised, is [that] beneath it rivers flow. Its fruit is lasting, and its shade. That is the consequence for the righteous, and the consequence for the disbelievers is the Fire.) (Al-Baqara: 285)
Because the talking is about something unseen, so Allah (swt) wants to bring it closer to our minds, for example, the Paradise contains wine, but it is not like the known wine in this world.
Concerning the unseen matters, there is no one more truthful than Allah (swt), as long as you believe in Allah (swt) mentally, you must believe that the Qur’an is from Allah, that our master Muhammad is the Messenger of Allah, and that all the Prophets are from the chosen Prophets of Allah (swt):
آمَنَ الرَّسُولُ بِمَا أُنزِلَ إِلَيْهِ مِن رَّبِّهِ وَالْمُؤْمِنُونَ ۚ كُلٌّ آمَنَ بِاللَّهِ وَمَلَائِكَتِهِ وَكُتُبِهِ وَرُسُلِهِ لَا نُفَرِّقُ بَيْنَ أَحَدٍ مِّن رُّسُلِهِ ۚ وَقَالُوا سَمِعْنَا وَأَطَعْنَا ۖ غُفْرَانَكَ رَبَّنَا وَإِلَيْكَ الْمَصِيرُ
(The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have believed in Allah and His angels and His books and His messengers, [saying], “We make no distinction between any of His messengers.” And they say, “We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination.”) (Al-Baqara: 285)
They say: “We hear and we obey”, not: “We hear and we do not obey” as the Jews did. Hence, believing in the unseen matters is an integral part of believing in Allah (swt). Believing in His angels, His Books, His messengers and the Day of Judgement are all of the unseen.
 Sahih al-Bukhari: Book of beginning of Cretion, Chapter of Description of the Paradise and that it is a creation, Hadith No. 3072.