This verse is somewhat similar to 2.21 and 26, where Samuel’s growth is also mentioned, although a different verb is used in 2.26. Here the idea seems to be that he grew to adulthood.

The LORD was with him: this is a common expression in the Old Testament (Gen 26.3; 31.3; Exo 3.12; Josh 1.5; and many other passages), indicating that God provides protection, guidance, and success.

The LORD … let none of his words fall to the ground is a literal translation. This Hebrew idiom means that God does not allow something to remain unfulfilled (see Josh 21.45; 23.14; 1 Kgs 8.56, for a similar expression). According to Deut 18.21-22, the sign of a true prophet is that, when he or she prophesies in the name of the LORD, the prophecy comes true. The sense here in verse 19 is that God “did not leave any of Samuel’s predictions unfulfilled” (New Jewish Publication Society’s Tanakh) or “he did not let any of Samuel’s messages fail to come true” (New Century Version). A literal rendering of these words will probably need to be avoided in most languages.

Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on the First and Second Books of Samuel, Volume 1. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here .