Is Da‘wah considered an act of worship on the basis that acts of worship include practice of everything that Allaah The Almighty loves, whether a deed or a saying, overt or covert?
If it is an act of worship, why is Da‘wah mentioned separately when describing the Muslim nation as a nation of worship and Da‘wah?

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 is His slave and Messenger.

Da‘wah (calling to Islam) is one of the best acts of worship for those who seek closeness to Allaah The Almighty. Therefore, Allaah The Almighty selected for this task His Prophets and Messengers, and He made their followers their inheritors. Allaah The Almighty Says what means: {And who is better in speech than one who invites to Allaah and does righteousness and says, "Indeed, I am of the Muslims."} [Quran 41:33] Indeed the Prophet, sallallaahu ‘alayhi wa sallam, was reported to have mentioned that scholars are the inheritors of the prophets. [At-Tirmithi and others. Al-Albaani: Saheeh]

Describing the Muslim nation as a nation of worship and Da‘wah may be a means to attract Muslims’ attention to the importance and merit of Da‘wah as an act of worship, in the same way that Allaah The Almighty Says (what means): {Whoever is an enemy to Allaah and His angels and His messengers and Gabriel and Michael - then indeed, Allaah is an enemy to the disbelievers.} [Quran 2:98] In this verse Allaah The Almighty mentioned Jibreel (Gabriel) and Mikaa’eel (Michael), may Allaah exalt their mention, after mentioning the angels, even though they are definitely among the angels. In this context, they were given special mention.

The description of the Muslim nation as a nation of worship and Da‘wah may be intended to explain to those who wrongfully believe that the practice of Islam is limited within performing outward rites such as prayer and pilgrimage,   that Islam is a comprehensive religion that combines outward rites, Da‘wah as well as numerous other branches of faith.

Allaah Knows best.