Japheth's enlargement — spread, growth, territory — is tied to his sharing in the blessing of Shem. Theologically, this foreshadows the inclusion of the nations (Gentiles, represented by Japheth) in the blessing of Abraham's line (Shem).
Memory phrase: God's blessing is wide enough for everyone.
Talk about it: Why do you think Japheth was welcomed into the blessing even though the special promise was with Shem?
Prayer: God, thank You that Your blessings are for everyone who chooses to honor You.