Bukhari

Hadith Commentary:

This captivity becomes a supreme blessing for them.
They attain eternal reward and everlasting felicity by embracing Islam.
The Messenger of Allah (sallallahu alayhi wa sallam) said: "You are the ones who complete the number seventy among the nations."
Sixty-nine nations have passed before you.
Among all these nations, you are the best nation in the sight of Allah. All the peoples of human history are included among these nations, whether they are Indian, Sindhi, Arab, or English—all are included in this.

Hadith Commentary:
➊
This hadith has also been narrated by Abu Hurairah (radi Allahu anhu) from the Messenger of Allah (sallallahu alayhi wa sallam), who said:
"Allah, the Exalted, is amazed at those people who will enter Paradise in chains."
(Sahih al-Bukhari, al-Jihad wal-Siyar, Hadith: 3010)
Sayyiduna Umar (radi Allahu anhu), while explaining this, says:
If Allah, the Exalted, had willed, He would have said:
(أَنْتُمْ خَيْرَ أُمَّةٍ)
Then all of us would have become the best community, but Allah, the Exalted, said (كُنْتُمْ),
thus this distinction is only for the Companions of Muhammad (sallallahu alayhi wa sallam) and those who follow in their footsteps.

➋
From this explanation, it is understood that this verse is for the noble Companions (radi Allahu anhum ajma'in), meaning that among the entire Ummah, the Companions (radi Allahu anhum ajma'in) are the best people. Whereas Ibn Abbas (radi Allahu anhu), in the explanation of this verse, says that by this are meant those Companions who migrated with the Messenger of Allah (sallallahu alayhi wa sallam).
(Fath al-Bari: 8/283)
According to this explanation, this verse becomes even more specific.
Accordingly, the meaning would be that among the Companions, those individuals are the best who had the honor of migrating with the Messenger of Allah (sallallahu alayhi wa sallam).
According to our inclination, this verse should be left upon its generality and the entire Ummah of Muhammad should be understood by it.
Thus, from the statements of Ubayy ibn Ka'b (radi Allahu anhu), Ikrimah, and Mujahid (rahimahullah) and others, it is evident that the entire Ummah is meant by this. As for the meaning of (كَانَ),
in such contexts, the mention or omission of (كَانَ)
is equivalent, as in the Qur'an:

And in another place:

The meanings of both these verses are the same. Also, in the hadith:
"My Ummah has been made better than all other communities."
(Musnad Ahmad: 5/383)
Therefore, it is better that by (خَيْرَ أُمَّةٍ)
the entire Ummah of Muhammad is meant, but conditionally, as we have mentioned earlier.

➌
The greatest benefit of this Ummah is that it brings people into Islam through jihad, by which they attain happiness in this world and the Hereafter.
This point is clearly indicated in the hadith.
And Allah is the One whose help is sought.