וְעַתָּ֣ה ׀ תֶּחֱזַ֣קְנָה יְדֵיכֶ֗ם וִֽהְיוּ֙ לִבְנֵי־חַ֔יִל כִּי־מֵ֖ת אֲדֹנֵיכֶ֣ם שָׁא֑וּל וְגַם־אֹתִ֗י מָשְׁח֧וּ בֵית־יְהוּדָ֛ה לְמֶ֖לֶךְ עֲלֵיהֶֽם׃ (פ)
Now therefore let your hands be strong, and be ye valiant; for Saul your lord is dead, and also the house of Judah have anointed me king over them.’
Malbim
Magnifies: And proportional to the greatness of gratitude, so shall the salvation increase in each and every moment... So that [God] shall magnify the salvations of God's king: and, external to how God will repay me for gratitude and praise, [God] will perform [acts of] lovingkindness for God's anointed one, for David and for his seed, for the faithful [acts of] lovingkindness of David [included] the cutting him of the covenant that sovereignty would not depart from his seed, and this is out of lovingkindness, as is written in II Samuel 2:7ff, and this lovingkindness shall continue for eternity.
Ralbag
If he shall show himself a worthy man, there shall not a hair of him fall to the earth: This means, "If he will put forth his strength to be a servant of the king and his commands like a worthy man, no harm will come to him for my part." And thus David sent to the men of Jabesh-Gilead, "Now therefore let your hands be strong, and be ye valiant." (2 Samuel 2:7)