See his autobiography, Contradictions (1974).
The three key factors in writing the language were reliability, efficiency, and machine-independence. The language is designed to allow aerospace-related tasks (such as vector/matrix arithmetic) to be accomplished in a way that is easily understandable to people who have spaceflight knowledge, but may not necessarily have proficiency with computer programming.
HAL/S is designed without many of the constructs that are known to be the cause of many errors. There are no abbreviations for keywords, and keywords are all reserved so that they cannot also be used as variables.
Some features, such as "GOTO" are provided chiefly to ease mechanical translations from other languages.
Considerations such as this are designed to reduce the chances of errors occurring, and also make it easy for others to read and understand the programs produced (self-documenting code).
HAL is not an acronym. On the Preface page of the HAL/S Language Specification, it says,
One particularly interesting feature of HAL is that it supports a three-line input format in which three source code lines are used for each statement, with the first and third lines usable for superscripts (exponents) and subscripts (indices). This was designed to be similar to mathematical notation.