What do the following words in "bold" mean?:

"Therefore it is of faith, that it might be by grace; to the end the promise might be sure to all the seed; not to that only which is of the law, but to that also which is of the faith of Abraham; who is the father of us all" (Ro.4:16).

Is not Paul saying that the only way of receiving the promise which is consistent with "grace" is receiving it by "faith"?

Many people define "grace" as "unmerited favor." And there is no merit in believing the gospel which is absolutely true and comes in power and in the Holy Spirit (1 Thess.1:5).

So that is why Paul writes that it is of faith THAT IT MIGHT BE BY GRACE.