“I will give them one heart.” Ezekiel 11:19 is very similar to Ezekiel 36:26. Also, it has some things in common with Jeremiah 32:39, see commentary on Jeremiah 32:39.
“I will put a new spirit inside you.” Ezekiel 11:19 has a couple important meanings, based on the word “spirit.” The word “spirit” can mean one’s thoughts, attitudes, and emotions, and it means that here, as we can tell from the whole verse. In the future, when the New Covenant is fully realized, people will have new thoughts and attitudes. This same truth is express in Ezekiel 36:26.
Also, however, “spirit” refers to the holy spirit of God, which in the Old Testament God placed “upon” people but which in the New Covenant will be “in” people. Jesus Christ understood this and taught it to his apostles at the Last Supper (see commentary on John 14:17).