、、。
The first step was visiting Jerusalem, the holy land of the three great religions.
Literal
First-step [topic-は], three-great-religions [genitive-の] holy-land, Jerusalem [object-を] visit [thing-こと] was.
A travel-writing opener. 手始め (てはじめ) is 'the first step,' 'the beginning (of a process),' with the nuance of 'to start things off.' The predicate structure ~は~を訪れることだった ('the X was to visit Y') uses こと to nominalize the verb phrase, turning a verbal idea ('visit Y') into a noun that can be equated with the subject ('the first step was X'). 三大宗教 ('three great religions') is the standard Japanese shorthand for the three major world religions — typically taken to mean Christianity, Islam, and Judaism in a Jerusalem context, or Christianity, Islam, and Buddhism in a global one. The apposition 三大宗教の聖地、エルサレム places the description first and the name second, the inverse of English conventions.