enduring while the world lasts (idiom); eternal
天 · 4 strokes
Depicts a person (大) with an emphasized head. Based on the original meaning "head". The meaning later shifted to "top", "high", and "sky".
长 · 4 strokes
Pictograph of an old person with long hair using a cane to walk. The simplified character 长 was adapted from the cursive form of the traditional character 長.
地 · 6 strokes
Phonosemantic compound. 土 represents the meaning and 也 represents the sound.
久 · 3 strokes
Depicts an arrow nock. The nock is the part of an arrow that is held against the bowstring before being launched. Same origin as 氒. The current meaning is a phonetic loan.
祝你们的友谊天长地久。
May your friendship last forever.