Walking In Spirit

Walking in Spirit or walking with God simply means taking steps of faith (one step at a time).  Teaching about the basic doctrine gives you an understanding (milk). The strong meat is not what you are being taught, they are understanding you get by virtue of your walk with God. 

You walk with God when you put your faith to work. Every successful faith-work you do imparts you with an extra ordinary understanding (eg Hannah) that is ability to take a higher (unthinkable) step of faith. 

Abraham did not foolishly obey God but when he was at dilemma between the right thing (not listening to God) and the faith thing (obey God), he went because he had the understanding of who Isaac is (covenant child) and he knew that even if he died , God is able to raise him up. He didn't go with the mentality of 'God said I should slaughter him', he went the mentality of 'God is able to raise the dead'. 

David had a leading in his heart to go and kill Goliath but he didn't go because of that; he went with the mentality that the God that delivered lion into his hand is able to make him triumph in everything. He went with the mind that Goliath was already a dead man since he had defiled the name of God (1Sam. 17:45; Gen 20:3).  

When you put your faith to work, you get a push spiritually. Strong meats are this kind of understanding you have which keeps giving birth to more understanding. This is how you grow spiritually (continuous walk in the spirit), this is how you build enough muscle to manoeuvre your way spiritually. Spiritual growth is measured by the level of understanding. This is what an unbeliever can not bear.