Sights and triggers: the smallest definition of marksmanship. Rightly applied, these two things are all that's needed to put accurate fire on a target. That's not at all to say that's all that's needed... As soon as more than one round is required, principles of grip and stance become the most important thing to presenting and controlling that firearm. Each of these can fill whole books with nuance, variations, and context, and should be addressed to that level. In a similar way, theology can be summed up in carefully concise ways. Salvation (saving faith in Jesus Christ) could be described as 1: man's inadequacy (sin), and 2: the Savior, Christ Jesus. Sinner and savior: the sights and triggers of salvation. Man as a fallen creature incapable of saving himself from the just punishment for sin, and God's calling of salvation and redemption in his Son.
Similarly to our first example, while these two things are the fundamentals of the faith and a good summary... that's only part of the story. I pray that after you read this you would think on your eternal state. If you have professed faith in Christ, then good... but now the war begins: Seek out a faithful church and brothers and sisters to fight alongside you. Seek out the training you need to serve God's kingdom, and discipline yourself as a warrior for Christ.