Verb
(transitive, idiomatic) To commit to something or someone firmly and resoundingly.
(transitive, idiomatic) To involve an individual or a thing in a plan or system in a way that escaping from it is difficult.
Source: en.wiktionary.orgPlaying the guitar, you kind of lock into a rhythm and a groove, and then it relaxes me to make up lyrics and sing. Cat Power
In the theater, it's a visceral and physical response because you move around so much. You have to do something physical to pull you in. On TV or in movies, everything is so small. You can just lock into a character and ease yourself into that way. LaTanya Richardson
If you wait to see how much money you have left at the end of the month to put toward savings, the answer may be zero. So, set up an automated monthly transfer from your checking to savings account. Once you lock into that commitment, you'll be forced to scale back spending to make ends meet. Suze Orman