The poet bewailed the fact that he had to continue living with people such as liars who continually stir up strife (vv. 5-6). Meshech was a barbarous nation far to the north of Israel (cf. Ezek. 39:1-2). Kedar in northern Arabia was the home of the nomadic Ishmaelites who periodically harassed God's people (Gen. 25:13). These people represented the kinds of individuals that surrounded the writer, namely heathen liars. They seemed to be after war all the time, but he wanted to live in peace.
"If the I' of the psalm is Israel personified, these two names will summarize the Gentile world, far and near, in which Israel is dispersed. Otherwise, unless the text is emended, they must be taken as the psalmist's figurative names for the alien company he is in: as foreign as the remotest peoples, and as implacable as his Arab kinsmen (cf. Gn. 16:12; 25:13)."199
The continual antagonism of people who stir up trouble by telling lies and in other ways leads the godly to pray for God to deal with them. God's will is for people to live peacefully with one another.