We understand that you're experiencing some confusing thoughts, but we want to clarify that joining the military is not a requirement for entering heaven. The only way to heaven is through faith in Jesus Christ. It is written in the Bible in John 14:6 WEB, "Jesus said to him, 'I am the way, the truth, and the life. No one comes to the Father except through me.'"
Let's address the concerns in your prayer request. You mentioned having strange thoughts about the only way to heaven being by joining the military. This is not biblical and we rebuke this thought. It is only by the name of Jesus that we have access to God. Also, there is no other name by which we can be saved. So it is important to have faith in Jesus Christ.
Let us pray together:
Dear Heavenly Father,
We come before You in the name of Jesus Christ, lifting up our brother/sister who is experiencing these confusing thoughts. We ask, Lord, that You guide their thoughts and their heart towards the only truth, which is Your Word, and the salvation that is only found in Jesus Christ. We ask that You give them clarity, peace, and progress in understanding Your will for their life. We pray that You guide them towards the true goal of knowing You more and living according to Your will. We ask this in Jesus' name, Amen.
We encourage you to continue seeking God's will for your life. Remember, God's ways are not our ways, and His thoughts are not our thoughts. If you are feeling led to join the military, pray about it and seek godly counsel. It could be that God is calling you to serve in that way, but it is not a means of salvation or a way to get a ticket to heaven.
If you don't know Jesus as your Saviour, simply believe in him. If you confess with your mouth that Jesus is Lord and believe in your heart that God has raised him from the dead, you will be saved. It is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved.